Genistein and daidzein belong to a large group of compounds called phytooestrogens present in several plants consumed by animals. Apart from oestrogenic activity, these compounds influence on many different processes in the organism. Their effect on metabolic processes was previously observed, however, it is poorly understood. In the performed experiment the effect of genistein (5 mg/kg BW) or daidzein (5 mg/kg BW) administered intragastrically for three days to growing male rats was studied and compared to oestradiol (0.1 mg/kg BW). Both phytooestrogens and oestradiol caused slight increase in blood glucose content with concomitant drop in insulin level. Blood cholesterol and HDL-cholesterol were not statistically altered. However, a slight reduction in total cholesterol with simultaneous slight rise in HDL-cholesterol in rats receiving oestradiol and phytooestrogens caused that HDL-cholesterol/total cholesterol ratio was significantly higher in these animals. The tested substances had no influence on blood free fatty acids and triglycerides. All these compounds caused substantial diminution in muscle triglycerides content. Liver glycogen, triglycerides and cholesterol contents were augmented only by daidzein. Our results indicate that genistein and daidzein evoked many similar metabolic changes. These changes were comparable to those caused by oestradiol and to changes induced by genistein and observed previously in ovariectomized rats.