Genetical differences in changes in blood pressure (BP) were chronologically investigated during pregnancy in stroke-prone spontaneously hypertensive rats (SHRSP), Wistar-Kyoto rats (WKY) and Sprague-Dawley (SD) rats. Especially, the early stages were carefully studied. Maternal conditions in SHRSP were modified by the treatments with NaCl and taurine, respectively. BP in SHRSP and WKY rose significantly at the early stage of pregnancy compared to prepregnancy levels (SHRSP; 208 +/- 2 mmHg vs 197 +/- 5 mmHg, WKY; 133 +/- 2 mmHg vs 126 +/- 1 mmHg) (p less than 0.05). In contrast, no such changes were observed in SD rats. Differences in 24-hour urinary epinephrine excretion before and during pregnancy ran parallel with such BP changes among these strains. NaCl-loaded SHRSP died during pregnancy with severe pathohistological changes in their kidneys and severe proteinuria. Taurine treatment had a marked prophylactic effect on these maternal pathological changes during pregnancy, resulting in better growth in offsprings. These results suggest that SHRSP could be one of the suitable animal models for the studies on toxemia of pregnancy and also suggest an important role of hypertensive genetical disposition in the development of toxemia of pregnancy.