We have previously described elevated Lii -Nao countertransport (CT) and Na-K cotransport (CO) in red cells of Caucasian patients from Boston. In this study, we report both transport systems in black patients from Philadelphia. The maximal rate (Vmax) of CT was assayed by measuring the Nao-stimulated Li efflux from cells containing +/- 6 mmol Li/liter. The Vmax of outward cotransport was assayed by measuring the furosemide-sensitive component of Na and K efflux into Mg medium from cells containing 50 mmol/liter of both ions. The mean value of CT for 18 normotensive (NT) subjects with no family history of hypertension, (-) FHH , was 0.18 +/- 0.05 (mmol/liter cells X hour); and in 14 hypertensive (HT) patients, 0.18 +/- 0.07. The mean values of Na and K cotransport were, respectively (mmol/liter cells X hour), in 18 NT subjects with (-) FHH , 0.38 +/- 0.24 and 0.50 +/- 0.28 in 18 HT subjects, 0.25 +/- 0.17 and 0.24 +/- 0.14. We conclude that there is no difference in the Vmax for CT between the two groups of black subjects, but that the Vmax for Na-K CO was significantly reduced in the HT group. Notably, the offspring of HT patients (age 14 years, n = 17) also had a marked reduction in the Vmax of Na (0.15 +/- 0.17) K cotransport (0.19 +/- 14) in comparison with the mean value of Na (0.40 +/- 0.2) and K (0.60 +/- 0.3) cotransport measured in offspring (n = 10) of NT subjects (age 14 years).(ABSTRACT TRUNCATED AT 250 WORDS)