Calretinin is a calcium-binding protein expressed abundantly in the central and peripheral neural tissues. It has been demonstrated to be a valuable marker in human testicular neoplasia. The immunohistochemical expression of calretinin has been studied in 102 samples of normal (n=25) and three different neoplastic canine testicular tumours (n=77). In normal canine testis, calretinin expression was restricted to Leydig and Sertoli cells of the testis. In tumour tissues, calretinin expression was detected in all tumours investigated (interstitial cell tumours, seminoma, and Sertoli cell tumours), with a cytoplasmic and nuclear pattern of cellular distribution. The present work reports, for the first time, calretinin immunohistochemical expression in normal and neoplastic canine testis.