Abstract. Lymphocytes from 150 unrelated individuals, 100 atopics and 50 lepers of the general population, mainly Mestizo, were tested for seven HL‐A antisera. The results found in the atopics showed a significant excess for HA‐7, and, taken as a whole, the distribution of HL‐A antigens was in this group more similar to the Caucasian component of the Mestizo population than to the Indians. In the case of leprosy, the results were significantly low for HL‐A2 and HL‐A3, but many of the samples from the lepers had an abnormal behaviour, with low vitality, that made its classification difficult.