A hyperthermic shock (43 degrees C/30 min) enhances in somite stages of the chick embryo development the activity of the caudal morphogenetic system, manifested by intensive growth of the embryonic trunk. The exposure also induced the synthesis of heat shock proteins (HSP 70), A single administration of a bioflavonoid quercetin dissolved in DMSO to chick embryos in stages HH 10-11 (10-14 somites) prior to heat exposure inhibited both the growth acceleration and the HSP induction