diff --git a/docs/upgrades/upgrade_6.8.5-6.9.0.pl b/docs/upgrades/upgrade_6.8.5-6.9.0.pl
index 8d977aee4..ea68f897f 100644
--- a/docs/upgrades/upgrade_6.8.5-6.9.0.pl
+++ b/docs/upgrades/upgrade_6.8.5-6.9.0.pl
@@ -71,6 +71,7 @@ sub addWorkflow {
 		title varchar(255) not null default 'Untitled',
 		description text,
 		enabled int not null default 0,
+		isSerial int not null default 0,
 		type varchar(255) not null default 'none'
 		)");
 	$session->db->write("create table WorkflowActivity (
diff --git a/lib/WebGUI/Workflow.pm b/lib/WebGUI/Workflow.pm
index 5083d0fb9..76bec45ff 100644
--- a/lib/WebGUI/Workflow.pm
+++ b/lib/WebGUI/Workflow.pm
@@ -288,6 +288,10 @@ A boolean indicating whether this workflow may be executed right now.
 
 A string indicating the type of object this workflow will be operating on. Valid values are "none", "versiontag" and "user".
 
+=head4 isSerial
+
+A boolean indicating whether this workflow can be run in parallel or serial. If it's serial, then only one instance of the workflow will be allowed to be created at a given time. So if you try to create a new instance of it, and one instance is already created, the create() method will return undef instead of a reference to the object.
+
 =cut
 
 sub set {
@@ -298,6 +302,11 @@ sub set {
 	} elsif ($properties->{enabled} == 0) {
 		$self->{_data}{enabled} = 0;
 	}
+	if ($properties->{isSerial} == 1) {
+		$self->{_data}{isSerial} = 1;
+	} elsif ($properties->{isSerial} == 0) {
+		$self->{_data}{isSerial} = 0;
+	}
 	$self->{_data}{title} = $properties->{title} || $self->{_data}{title} || "Untitled";
 	$self->{_data}{description} = (exists $properties->{description}) ? $properties->{description} : $self->{_data}{description};
 	$self->{_data}{type} = $properties->{type} || $self->{_data}{type} || "none";
diff --git a/lib/WebGUI/Workflow/Instance.pm b/lib/WebGUI/Workflow/Instance.pm
index 7c1027608..b35a5d93a 100644
--- a/lib/WebGUI/Workflow/Instance.pm
+++ b/lib/WebGUI/Workflow/Instance.pm
@@ -41,7 +41,7 @@ These methods are available from this class:
 
 =head2 create ( session, properties [, id ] ) 
 
-Creates a new workflow instance.
+Creates a new workflow instance and returns a reference to the object. Will return undef if the workflow specified is serial and an instance of it already exists.
 
 =head3 session
 
@@ -62,6 +62,9 @@ sub create {
 	my $session = shift;
 	my $properties = shift;
 	my $id = shift;
+	my ($isSerial) = $session->db->quickArray("select isSerial from Workflow where workflowId=?",[$properties->{workflowId}]);
+	my ($count) = $session->db->quickArray("select count(*) from WorkflowInstance where workflowId=?",[$properties->{workflowId}]);
+	return undef if ($isSerial && $count);
 	my $instanceId = $session->db->setRow("WorkflowInstance","instanceId",{instanceId=>"new", runningSince=>time()}, $id);
 	my $self = $class->new($session, $instanceId);
 	$self->set($properties);