Chronic renal failure was induced in 10 Wistar rats using a lithium-containing (40 mmol/kg) diet from time of birth until an age of 55-65 weeks. Nine Wistar rats served as controls. The plasma lithium, the plasma urea, and the inulin clearance were measured, and one kidney was fixed by vascular perfusion with glutaraldehyde. The number of glomeruli was estimated stereologically by the fractionator method. The total number of glomeruli per kidney was 23.9 x 10(3) +/- 3.65 x 10(3) (+/- SD) in controls and 22.0 x 10(3) +/- 1.48 x 10(3) in the lithium-treated group, showing no statistically significant difference. The mean glomerular volume was also estimated using stereological methods. The number-weighted mean volume was reduced by 42% in the lithium-treated group, whereas the volume-weighted mean volume was unchanged. This can be attributed to the occurrence of many small glomeruli and a few very large glomeruli in the lithium-treated group. The many small glomeruli have in a previous study been shown to be atubular. The present study showed that the glomerular population is quite resistant to the deleterious effect of lithium; thus glomerular atrophy was seen, but no loss of glomeruli occurred.