Never having looked at an immigrant record I don't know. However, my guess is it refers to the original source of that particular record and somewhere there is guide to the source code. Where did you get the immigrant record? Look at the beginning of your source and see if there is legend or list of source codes. There is a book called 'Passenger and Immigration Lists Bibliography, 1538-1900' by P. William Filby and it lists about 2600 published sources. Each source has a number. It is considered THE most comprehensive [but is certainly not the only] list of such records. He also has an ongoing work indexing all published lists. Dource codes could refer to numbers in Filby's book or another similiar book. Cheryl Rothwell clrothwell@mindspring.com