An instrument providing cyclic stress to cells cultured in vitro has been developed. The unit uses a vacuum to deform a plastic Petri dish yielding 0·13 % compression to cells on the inner surface, measured by strain gauge recordings. A regimen of 25 s stress and 5 min relaxation induced no significant change in synthesis of a 45x103Mr protein that comigrates with actin, whereas a 52x103Mr protein that comigrated with tubulin decreased from 12·7 ± 0·451 % of the total protein synthesized in control, static cells to 8·53 ± 0·182% in stressed cells. The unit may have a broad application in monitoring biochemical changes in response to stress in cells such as muscle, lung, tendon, ligament and bone that are normally subjected to tension or compression.