All three agents acted equipotently in eliciting positive immediate skin reactions from all subjects tested. Each agent demonstrated 10 mm of net whealing at 5 to 10 ìg base (16. 7 to 40. 4 nmol) injected intradermally. The ability to elicit immediate skin test reactions with endogenous opioid peptides was examined with the use of dynorphin, [D-Ala, 2-D-Leu5] enkephalin.