Thanks both for the suggestions. Having tested with values in the split function I had it produced the values I was expecting. The key was the varchar v char data length. I'd originally written the stored procedure to expect one value as the field was 6 characters in length. When it was converted to take multi valued parameters I forgot to change that. The split function worked fine. Sometimes you need someone else to look at your code before you see the obvious! At least I know how to do this now until Microsoft make this a little more user-friendly from within ssrs.