A prolonged exposure of larvae of the greater waxmoth, Galleria mellonella, to a sub-physiological temperature (0 C) initiated an induction of proteosynthesis of gamma globulins in the haemolymph. In vivo administration of inhibitors of transcription and translation, respectively, prevented the cooling shock induction of the new gamma globulin protein fractions. In addition, the oxygen consumption at this temperature revealed an immediate decrease reaching its minimal value in about an hour. The remaining consumption of oxygen at this low temperature, however, represents an evidence of sufficient biochemical conditions for a de novo proteosynthesis of gamma globulins. In a reverse situation (transfer from 0 C to 30 C) the larvae regained the original levels of the oxygen consumption in approximately 40 minutes. The osmotic pressure of haemolymph also exhibited dramatic changes in response to the exposure to low temperature. The de novo synthesis of the gamma globulin fractions in the haemolymph represents one aspect of insect adaptation to cold.