diff --git a/lib/manifest_processor.py b/lib/manifest_processor.py
index 890e75e..3b9d704 100644
--- a/lib/manifest_processor.py
+++ b/lib/manifest_processor.py
@@ -39,6 +39,10 @@ def __init__(self, username=None, password=None, google_client_secrets=None,
 
         self.password = password
 
+        # By default, we will check MD5 checksums after each file is
+        # retrieved/downloaded.
+        self.validation = True
+
         if google_client_secrets is not None and google_project_id is not None:
             self.logger.info("Create GCP client.")
             from gcp import GCP
@@ -152,6 +156,15 @@ def _get_s3_obj(self, url, file_name):
 
         return result
 
+    # Method to turn off MD5 checksum checking after a file is downloaded.
+    # For large files and particularly with manifests that contain large
+    # numbers of large files, disabling validation may significantly boost
+    # performance.
+    def disable_validation(self):
+        self.logger.debug("In disable_validation.")
+
+        self.validation = False
+
     # Function to download each URL from the manifest.
     # Arguments:
     # manifest = manifest list created by functions in convert_to_manifest.py
@@ -221,17 +234,24 @@ def download_manifest(self, manifest, destination, priorities):
                     failed_files.append(2)
                     continue
 
-                # Now that the download is complete, verify the checksum, and then
-                # establish the final file
-                if self._checksum_matches(tmp_file_name, mfile['md5']):
+                if self.validation:
+                    # Now that the download is complete, verify the checksum, and then
+                    # establish the final file
+                    if self._checksum_matches(tmp_file_name, mfile['md5']):
+                        self.logger.debug("Renaming {} to {}".format(tmp_file_name, file_name))
+                        shutil.move(tmp_file_name, file_name)
+                        failed_files.append(0)
+                    else:
+                        print("\r")
+                        msg = "MD5 check failed for the file ID {0}. " + \
+                              "Data may be corrupted."
+                        print(msg.format(mfile['id']))
+                        failed_files.append(3)
+                else:
+                    self.logger.debug("Skipping checksumming. " + \
+                                      "Renaming {} to {}".format(tmp_file_name, file_name))
                     shutil.move(tmp_file_name, file_name)
                     failed_files.append(0)
-                else:
-                    print("\r")
-                    msg = "MD5 check failed for the file ID {0}. " + \
-                          "Data may be corrupted."
-                    print(msg.format(mfile['id']))
-                    failed_files.append(3)
 
         return failed_files
 
diff --git a/lib/portal_client.py b/lib/portal_client.py
index 755bc5d..2280176 100644
--- a/lib/portal_client.py
+++ b/lib/portal_client.py
@@ -31,22 +31,27 @@ def parse_cli():
                     'generated from a portal instance.'
     )
 
-    group = parser.add_mutually_exclusive_group(required=True)
-
-    group.add_argument(
+    parser.add_argument(
         '-m', '--manifest',
         type=str,
         help='Location of a locally stored manifest file from.'
     )
 
-    group.add_argument(
+    parser.add_argument(
         '-u', '--url',
         type=str,
         required=False,
         help='URL path to a manifest file stored at an HTTP endpoint.'
     )
 
-    group.add_argument(
+    parser.add_argument(
+        '--disable-validation',
+        dest='disable_validation',
+        action='store_true',
+        help='Disable MD5 checksum validation.'
+    )
+
+    parser.add_argument(
         '-t', '--token',
         type=str,
         required=False,
@@ -184,6 +189,11 @@ def main():
     mp = ManifestProcessor(username, password,
             google_client_secrets=client_secrets, google_project_id=project_id)
 
+    # Turn off MD5 checksumming if specified by the user
+    if args.disable_validation:
+        logger.debug("Turning off checksum validation.")
+        mp.disable_validation()
+
     while keep_trying:
         manifest = {}
 
diff --git a/setup.py b/setup.py
index 67fc8be..c663010 100644
--- a/setup.py
+++ b/setup.py
@@ -9,7 +9,7 @@ def read(fname):
 setup(name='portal-client',
       description='Download client tool for IGS Portal servers.',
       long_description=read('DESC'),
-      version='1.3.0',
+      version='1.4.0',
       py_modules=['portal_client'],
       author='Victor F',
       author_email='victor73@github.com',