Urinary levels of DHA and oestrogens were determined in normal, unilaterally and bilaterally cryptorchid boars and in such animals following hemicastration or treatment with hcg. Removal of one testis from normal boars or the abdominal testis from unilaterally cryptorchid boars did not appreciably alter the urinary levels of DHA and oestrogens. Removal of the scrotal testis of unilaterally cryptorchid boars or one abdominal testis of bilaterally cryptorchid boars resulted in a significant drop in urinary steroid values. Except for one boar, DHA returned to within control levels in 2 months while oestrogen values were significantly lower in two animals and significantly higher in one animal at 2 months. hcg treatment caused a highly significant increase in DHA and oestrogen excretion in a normal boar and a unilaterally cryptorchid boar with a scrotal testis remaining after hemicastration. Boars with bilateral cryptorchid testes and a boar with an abdominal testis remaining after hemicastration showed a limited response to hcg injections. The results suggest that the cryptorchid testis of the pig is able to compensate for the loss of the contralateral gonad but the limit of response to gonadotrophin is very much lower and the time of response is slower than that exhibited by the scrotal testis.