The aim of the present study was to compare yellow jacket venom extracts from two different companies and to compare skin prick test (SPT) with intradermal test (IDT). IDT and SPT with yellow jacket venom (ALK and Pharmacia Reless(R)) were performed on 54 yellow jacket allergic patients and 44 symptom-free volunteers. Venom was diluted to 300, 100, 10 and 1-mu-g/ml for SPT and 10(0), 10(-1), 10(-2), 10(-3) and 10(-4)mu-g/ml for IDT, according to the manufacturers' instructions. Skin tests were performed on both forearms. Both extracts showed approximately the same relationship between sensitivity and specificity, but the Pharmacia Reless yellow jacket venom extract showed a 5- 10 fold higher biological activity in both SPT and IDT. Thus yellow jacket venoms of ALK and Pharmacia Reless are not comparable in allergen activity at the same venom concentrations. Using extracts from the same company, SPT and IDT were comparable with regard to sensitivity and specificity at an allergen concentration 1000 times higher for SPT than for IDT.