In order to determine the effect of X-irradiation on intracellular signal transduction in mouse oocytes and embryos, JNK, ERK and p38 kinase activities were measured by the state of phosphorylation of their respective substrates (c-Jun, Elk-1 and ATF-2, respectively) in two mouse strains differing in radiation sensitivity, namely C57BL and BALB/c. In a first step, control oocytes and embryos were compared for their respective kinase activities at various stages of oocyte maturation (germinal vesicle and metaphases of 1st and 2nd meiosis stages) and early embryonic development (1-, 2-, 4-, 8- and 16-cell, morula and blastula stages). Levels of p38, ERK or JNK kinase activities were shown to vary with the stage of oocyte maturation and embryo development. In a second step, 1- and 2-cell embryos were X-irradiated with 2.5 Gy during the S-phase of the 1st or the 2nd cell-cycle, respectively. There were no significant differences in p38, ERK and JNK kinase activities between control and irradiated embryos, whatever the stage or mouse strain was considered. In conclusion, p38, ERK and JNK kinase activities were shown to vary during oocyte maturation and early embryonic development. Apparently, X-irradiation did not affect these kinase activities at the 1- and 2-cell stages in either mouse strains regardless of their difference in radiation sensitivity.