The study uses immunological techniques to measure stress protein concentrations in Mytilus to examine the persistence of the heat-shock response over time. Metabolic labeling and two-dimensional electrophoresis demonstrated that three major stress protein groups, hsp60, hsp70, and the low molecular weight stress proteins, were rapidly synthesized immediately after transfer to a higher temperature. The concentrations of hsp60 and hsp70 were then measured at various times up to 8 weeks after transfer from 17 C to 27 C, a temperature they can encounter for long periods in their environment. Concentrations of both stress proteins increased within a few hours of the transfer and remained significantly elevated compared to controls for the two-month duration of the experiment. (Copyright (c) 1992 Blackwell Scientific Publications, Inc.)