To clarify the functions of the agranular cells in the polar cushion of the juxtaglomerular apparatus, the effects of drinking 1% NaCl or eating a diet containing 8% NaCl were examined on the numbers of granular and agranular cells in the polar cushions, the kidney weights, and the blood pressures of male Sprague-Dawley rats after uninephrectomy. Only 11.8% of the cells in the polar cushions of control rats in this study were granular; hence, 88.2% of the cells were agranular. After uninephrectomy of rats on a normal diet with tap water, the maximal increase in relative weight of the remaining kidney occurred within 2 weeks, and the degree of hypertrophy was estimated as 64%. Rats with a high salt intake after uninephrectomy had a similar increase, indicating that a high salt intake after uninephrectomy did not affect the degree of hypertrophy of the remaining kidney. The mean juxtaglomerular cell count (JGCC) showed moderate increases 2 weeks after uninephrectomy. Drinking 1% NaCl for 2 weeks after uninephrectomy produced about twice as much increase in the JGCC. Maximal initial increases in JGCCs occurred at 2 weeks, well before an increase in blood pressure. Drinking 1% NaCl had no significant effect on blood pressure within 2 weeks, but there was a definite hypertension at 8 weeks, with no further increase in JGCC. On an 8% NaCl diet hypertension developed between 8 and 16 weeks, when the JGCC was greater than previous levels. Clipping the renal artery of a solitary kidney produced hypertension but no increase in JGCC within 2 weeks. Uninephrectomy lowered the mean granular cell count, and drinking saline lowered it even more. Hence, the proliferation involved agranular cells. In summary, excessive NaCl intake was associated with a rapid proliferation of agranular cells which was maximal at 2 weeks and occurred before any significant increase in blood pressure. This suggests that the agranular cells in the polar cushion of the juxtaglomerular apparatus are concerned more directly with sodium chloride metabolism than with blood pressure regulation.