The concentration of mRNA of insulin-like growth factor-II is (IGF-II) much elevated in some embryonic tumours such as Wilms tumour (nephroblastoma). In order to prove whether or not IGF-II is produced by the tumour tissue, IGF-II was extracted from freshly frozen tissue of Wilms tumour and hepatoblastoma. Normal adjacent tissue of kidney and liver was used as a control. The total IGF-II in Wilms tumour was 548.4 +/- 77.4 ng/g (n = 7) compared to 112.8 +/- 38.2 ng/g (n = 5) in kidney. In two hepatoblastomas, it was 96.1 +/- 22.8 ng/g compared to 30.1 +/- 14.2 ng/g in normal liver. Small pieces of fresh primary tissue of several Wilms tumours were successfully transplanted into immunodeficient nude mice. In serum of tumour-bearing mice IGF-II was elevated compared to normal mice. Liver weight of tumour bearing mice was higher than that of control mice (2.29 +/- 0.4 g and 2.02 +/- 0.06 g; P < 0.005). This was also found for kidney weight (0.58 +/- 0.01 g vs. 0.51 +/- 0.01 g in controls, P < 0.001). In contrast, serum glucose (9.73 +/- 0.29 mmol/l compared to 11.80 +/- 0.42 mmol/l in controls, P < 0.0005) was decreased. However, there was no significant difference in nose-tail length of tumour-bearing compared to control mice. These results demonstrate that besides the highly increased IGF-II-mRNA, the synthesis of the peptide IGF-II and its release into circulation are also elevated in Wilms tumour transplanted into nude mice.(ABSTRACT TRUNCATED AT 250 WORDS)