SummaryA study was made to establish the value of the leucocyte aggregation test (LAT) in drug allergy using penicillin antigen. The antigen‐induced human peripheral blood leucocyte aggregation was measured quantitatively. The results obtained have been compared with the leucocyte migration inhibition test (LMIT) in patients with or without delayed penicillin allergy. Among forty‐four penicillin‐allergic subjects and thirty‐six control subjects, LAT was found positive in respectively 70.5 and 30.5% (P<0.001) whereas LMIT was found positive in respectively 56.8 and 50% of the patients. These results were confirmed by multiple correspondence analysis (MCA), using a computer. Furthermore, this method, enables a more comprehensive and reliable interpretation of the tests, by the help of various quantitative and qualitative criteria.It is concluded that LAT shows more discrimination than the LMIT in distinguishing a penicillin‐allergic population from a non‐allergic one. In addition, LAT offers great technical advantages over the LMIT for the diagnosis of d