The effects of 1-4 days of fasting and 3-24 h of refeeding of 4-day fasted rats on the rate of [3H]-thymidine incorporation into DNA in vitro (referred to as DNA synthesis) and the activity of thymidine kinase and DNA polymerase were measured in the oxyntic gland mucosa. Ad libitum fed rats served as control. Starvation for 1-4 days significantly depressed the activity of mucosal thymidine kinase (39-58%) and DNA polymerase (26-36%), when compared with the initially fed control. Mucosal DNA synthesis, measured in 3- and 4-day fasted rats, was also markedly decreased (80-90%) compared to the fed control. Refeeding of 4-day fasted rats significantly stimulated DNA synthesis and the activity of thymidine kinase and DNA polymerase. However, whereas DNA polymerase and thymidine kinase attained their respective peak activity (84 and 340% above the 4-day fasted level) after 3 and 6 h of refeeding, DNA synthesis was significantly stimulated (700% above the 4-day fasted control) after 9 h of refeeding. Administration of actinomycin-D prior to refeeding reduced the magnitude of stimulation of mucosal thymidine kinase and the rate of DNA synthesis, but had no effect on DNA polymerase activity which was found to be stimulated to the level of non-antibiotic treated rats. The current results demonstrate that following refeeding mucosal DNA polymerase and thymidine kinase activities are increased before DNA synthesis is significantly stimulated. Blocking of the maximal stimulation of mucosal thymidine kinase lowers the magnitude of the subsequent rise in DNA synthesis caused by refeeding.