Correlation between the level of testosterone in blood plasma and serotonin content in hippocampus and frontal cortex was investigated in aggressive and submissive rats of different age groups. Dependence of the testosterone level on behavior type was found. The highest testosterone level was observed in aggressive animals. In submissive males we found considerable decrease of the serotonin level in frontal cortex and hippocampus as compared with balanced and aggressive ones. The positive correlation between testosterone and serotonin levels was shown in submissive and aggressive animals in contrast to the negative correlation in balanced males. The change in negative correlation between the testosterone and serotonin content into positive one in the aggregate with the decrease or the increase of testosterone level is likely to be one of the components in formation of submissive and aggressive (dominant) behavior type, respectively.