The kidney growth seen after the induction of experimental diabetes in rats has been compared to the compensatory renal growth after one-sided nephrectomy. After five days the kidney weight had increased from 650 +/- 15 mg in a group of controls to 778 +/- 21 mg in diabetic rats, and 764 +/- 17 mg in unilaterally nephrectomised rats. The increased weight was in both groups reflected in an increased DNA content and increased RNA/DNA and protein/DNA ratios. In a group of rats made diabetic and nephrectomised at the same time, kidney weight increased to 953 +/- 22 mg after five days. When rats were unilaterally nephrectomised after 20 days of untreated diabetes, compensatory growth was much more pronounced than in non-diabetic rats, kidney weight rising from 780 +/- 21 to 1144 +/- 39 mg in five days. Similarly, in rats with established compensatory renal hypertrophy, diabetes induced a very rapid growth of the remaining kidney (1226 +/- 46 mg after five days).