The morphology and proliferation of vascular smooth muscle cells (VSMC) were studied in cultures prepared from the aorta of newborn male and female Wistar rats. The doubling times (DT) of the male-derived population were 16.4+/-0.7 h and 30.0+/-2.2 h in the exponential and post-exponential growth phases, respectively. In the female donor cells, the corresponding DT values were significantly longer, i.e. 21.9+/-1.8 h and 38.0+/-2.2 h. In addition, the period of growth was shorter in the female-derived cultures. The percentage of 3H-thymidine labelled cells in male cultures was 61.0+/-3.1, 92.8+/-1.9 and 98.7+/-0.6% at 2, 27 and 52 h, respectively. In the female-derived populations, only 24.6+/-4.4, 66.1+/-3.8 and 82.8+/-2.0% of cells were labelled at the corresponding incubation intervals. As a consequence, the final population density in male cultures was 5.6 times higher. In addition, the male-derived VSMC were mainly spindle-shaped and bulgy in appearance while those from female donors were flat and polygonal which means that the cells were adhering to the growth support to a different extent. The study revealed early determination and long-term persistence of lower adhesiveness as well as higher growth potential of male VSMC, i.e. properties which may be of importance for explaining the higher incidence of vascular wall disorders in males.