Skin fibroblasts from newborn spontaneously hypertensive rats (SHR) grow faster in culture than Wistar-Kyoto rat (WKY) cells. Similar results have been described for vascular smooth muscle cells from prehypertensive and adult SHR. This suggests the existence of an intrinsic abnormality in vascular and nonvascular cells of mesodermal origin affecting cell growth control in those rats. In an attempt to determine the relation between high blood pressure and this trait, we cultured skin fibroblasts from adult SHR, WKY, F1, and F2 hybrid SHR/WKY populations by explant technique. Their growth capacity was determined by culture well DNA doubling time and by [3H]thymidine incorporation. Adult SHR fibroblasts grew more quickly (doubling time [DT] = 37.2 +/- 2.3 h, n = 8) than WKY ones (DT = 53.9 +/- 3.6 h, n = 6). Female SHR were crossed with male WKY to produce an F1 and an F2 hybrid generation presenting a Mendelian distribution of blood pressure. Skin fibroblasts were cultured from 21 rats belonging to the highest and the lowest blood pressure groups. No difference was observed between the two groups in either growth (DT = 47.5 +/- 4.1 h, n = 11 v DT = 44.6 +/- 3.2 h, n = 10) or epidermal growth factor-induced [3H]thymidine incorporation. These observations suggest that the increased growth capacity observed in SHR is not a determinant of high blood pressure initiation but may be involved in early cardiovascular enlargement.