The growth of the human gastric cancer cell line HGT-1 is regulated by a gastrin-like peptide through an autocrine process. In order to analyse the mechanism of action of this peptide, a study at different steps of the cell cycle was considered; so, a blocking of this cell line by thymidine or hydroxy-urea was studied by cytofluorimetry. In normal growth conditions in 10% FCS medium, 57% of the cells were in G0/G1 phase and 31% in S phase. A treatment with 2 mM hydroxy-urea followed by 4 hours in 10% FCS medium led to 85% of the cells in S phase. By successive treatments with thymidine and hydroxy-urea followed by 1 hour in 10% FCS medium, 2 peaks of S phase corresponding to 86% of the cells were observed; after 24 hours, cells were distributed as found for the unconfluent cell line, whatever the treatment. On the other hand, the thymidine kinase activity of unconfluent cells which was relatively elevated as compared to other cell lines (278 mU/mg protein), was increased by synchronisation with hydroxyurea followed by 1 hour in 10% SVF medium (338 mU/mg protein); after 8 hours in 10% FCS medium, this activity decreased at the value observed for cells treated with thymidine followed by 1 hour in 10% FCS medium (214 mU/mg protein). In conclusion, a synchronisation either by thymidine or by hydroxy-urea, led to a blocking of the HGT-1 cell line at different steps of the cell cycle, leading to a better knowledge of its autocrine growth regulation.