Punch biopsies taken 12, 24, 48, and 72 hours after skin testing with Leprosin A have been used to prepare ultrathin sections for the identification and enumeration of infiltration cells. The study was performed on small numbers of both healthy persons and leprosy patients with various forms of the disease living in India. Similar cells were found to infiltrate both positive and negative responses to the skin test reagent, although there were quantitative differences. The most striking findings were the absence of the expected basophils and an infiltration of eosinophils which proceeded to degranulate. This was especially noticeable in a healthy leprosy contact and in patients at the tuberculoid end of the leprosy spectrum, whether or not they produced positive skin reactions to Leprosin A. In patients at the lepromatous end of the spectrum, infiltrates were largely neutrophils.