The level of expression of the cell cycle regulatory proteins is an important facet in determining the malignant state. Fifty consecutive colectomy specimens of colorectal carcinoma in patients over 50 years of age, and 25 cases in patients under 30 years, were examined to ascertain retinoblastoma protein expression and to relate this to clinicopathological features. Retinoblastoma protein (pRb) staining was more intense in well differentiated, low stage carcinomas in the over 50 age group (p < 0.001). On the other hand, in the under 30 age group, pRb staining was seen in all tumours grades and stages. No statistical significance was noted with other clinical or pathological features in both age groups.