Dexamethasone (1 microM) decreased the distribution of cells in S phase (about 75%) and increased that of G1 cells (1.1-fold) in the DNA histogram of human submandibular salivary gland adenocarcinoma cells (HSG) reversibly. In synchronized cells at G1 phase, glucocorticoid delayed the initiation of DNA synthesis by about 3-4 h. The conditioned medium (50%) or exogenous human epidermal growth factor (EGF, 10 ng/ml) significantly nullified these effects by glucocorticoids. These results suggested that glucocorticoids arrested the cells at G1 phase, which implied the inhibition of production of some progressive factor, probably EGF, in the cell cycle of HSG.