An uncommon reaction to varicella vaccine has been urticaria. Based on two reports of urticaria believed to be due to gelatin in recipients of measles-mumps-rubella vaccine, we suspected gelatin as the cause of generalized urticaria in two children after varicella vaccination. Intradermal testing with gelatin yielded a wheal and flare reaction in both children. We conclude that children known to be allergic to gelatin should not receive Oka/Merck varicella vaccine (VARIVAX).