It is well established that muscle-relaxant drugs may be responsible for anaphylactoid reactions during anesthesia. In this study, we developed an in vitro test with a commercially available solid phase for the detection of specific IgE directed to the tertiary or quaternary ammonium groups of neuromuscular-blocking drugs. The solid-phase complex was P-aminophenylphosphoryl-choline (PAPPC) immobilized on agarose, and an RIA was performed with an antihuman IgE labeled with 125I. The results, expressed as the percentage of 125I-labeled anti-IgE linked to the solid phase, were at 0.41 +/- 0.19 for 34 control sera from nonallergic healthy adults, with an upper limit estimated at 1%. The values obtained with the sera of 31 allergic patients ranged from 0.6% to 41% with a sensitivity of 97%. The specificity and the positive predictive value of the PAPPC RIA were 97% and 94%, respectively. These results were compared with results of other RIAs with morphine, trimethylamine, triethylamine immobilized on epoxy-activated Sepharose, and choline hydrochloride immobilized on Sepharose (quaternary ammonium Sepharose RIA) and with Phadebas RAST succinylcholine and Phadebas RAST alcuronium. The PAPPC RIA appears to be the most efficient test to screen sera for the presence of IgE antibodies directed to neuromuscular-blocking drugs. One major advantage is that this solid phase is commercially available and ready to use. This advantage will improve the accuracy in the comparison of the results with results from different laboratories.