Starvation causes insulin resistance which is partly due to decrease of insulin action on glucose transport in target cells. Preliminary data from other authors suggest that starvation is associated with an increase of the time necessary for insulin to exert its maximum effect on glucose transport. In order to verify this finding, 3-O-methylglucose (3OMG) transport was studied in isolated rat adipocytes from starved and fed rats. The total intracellular space for 3OMG was not modified by 48h starvation. After 48h starvation, 3OMG transport into fat cells was less responsive to maximum insulin concentration than in controls: 33 +/- 2% (controls) vs 23 +/- 4% (starved) of total glucose space, p less than 0.05; the sensitivity to insulin was normal or even increased in comparison to controls: 50% of maximum effect was reached at 42 microU/ml insulin in controls and at 26 microU/ml insulin in starved animals. We could not find any effect of starvation on the time-response curves of insulin action.