AbstractDrosophila virilis stocks differing in reaction to high temperature (32°C) were studied. The sizes of the larval salivary glands, ring gland, and imaginal discs of the heat‐sensitive stock 147, whose pupal (p) esterase was activated at 32°C, were found to be significantly smaller at high temperature than at 25°C. In larvae of the heat‐resistant stock 101, whose p‐esterase was inactivated at 32°C, the salivary glands and imaginal discs were larger under conditions of high temperature than those of the control larvae. Treatment of stock 147 larvae with ecdysone at 32°C did not affect p‐esterase activity and was 100% lethal. By contrast, the juvenile hormone activated p‐esterase under these conditions and normalized the development of stock 147 larvae. A scheme is suggested for the role of p‐esterase in the regulation of the hormonal status of D. virilis under high temperature conditions.