We examined 69 biopsies of acne lesions known to be 6, 24 or 72 h old and found that the lymphocyte was the predominant cell at 6 and 24 h. The helper:suppressor T cell ratio in the inflammatory infiltrate was 2.8:1. Polymorphonuclear leukocytes were increasingly seen at 24 and 72 h and were associated with disruption of the duct. We hypothesize that this early lymphocytic infiltrate represents a cell mediated immune response to an antigen within the duct lumen.