An unusual population of the lycaenid butterfly, Meleageria daphnis (Lepidoptera: Lycaenidae), is found in the Kislovodsk area (43.8°N lat., 42.7°E long.) of southern Russia; 60% of the observed females in the adult population have been partial gynandromorphs or sexual mosaics during the period of 1988 to 1993. This site is within 30 km of the center of the refining area where uranium was processed for the first Soviet atomic bombs, and is also within the southeastern boundary (extent as of 2 May 1986) of the cloud of radiation released from the Chernobyl disaster on 26 April 1986. The situation may reflect a high level of radiation-induced somatic mutations or a genetic alteration in the Y-chromosome carried by most of the females in the population.