Disodium cromoglycate (DSCG) was used in a controlled laboratory study of an IgE-mediated, immediate-type, respiratory response in primates. The respiratory response to antigen was partially inhibited by DSCG. Systemic administration of DSCG did not inhibit active cutaneous reactivity to ascaris antigen or reverse passive cutaneous reactivity to anti-human IgE in rhesus monkeys, DSCG did not inhibit the respiratory eosinophil response which occurs after ascaris challenge in a highly reactive monkey. A possible explanation for the dissociation of the cutaneous and respiratory activity of DSCG in primate immediate-type responses may be the existence of more than one population of mast cells. The intravenous administration of DSCG resulted in transient aberrantly conducted premature beats in 3 normal rhesus monkeys.