Skin tests with opioid peptides naturally occurring in cow's milk: beta-casomorphin-7 and alpha-casein (90-95), were performed in 25 healthy children. Wheal and flare reactions, similiar to histamine and codeine were observed in all children. The area of these reactions was concentration dependent. Pretreatment with H1 antagonist--cetirizine significantly inhibited the skin response to both peptides. Beta-casomorphin-7 and alpha-casein (90-95) are noncytotoxic histamine releasers in humans.