Chick pineal cells in static culture display a persistent, photosensitive, circadian rhythm of melatonin synthesis and release. Melatonin synthesis and its rhythm are also sensitive to temperature changes. By SDS-PAGE autoradiography, we found that several heat shock proteins (HSPs 25, 70, and 90) are synthesized under temperature conditions which also cause changes in melatonin production and rhythms. We did not see substantial phase-dependent differences in the induction of HSP synthesis, nor did we detect any clear effect of light on the synthesis of these proteins.