American and (I think) French frontline is sold without an expiration date (incl on ebay), just storage instructions to keep fresh. UK frontline has one and a use by warning. I'd give Merial a ring on monday and ask them if it's safe or if it's exactly the same stuff as sold in those 2 countries at least (?). As it's used as the DEFRA passport approved "tick and parasite" treatment before coming back into the UK, it may be the same and the difference may be regulations; then again, I thought the regs were EU wide. I'd be careful, but then I'm a neurotic!