Colorectal adenocarcinomas may display features of endocrine differentiation, shown by argyrophil stains and by the expression of endocrine markers such as chromogranin A. We investigated chromogranin A and secretogranin II immunoreactivity in a series of 208 carcinomas of the large bowel to assess the prevalence and clinical significance of endocrine differentiation. Tumors expressing endocrine markers were classified as low expressors (< than 1 immunoreactive tumour cell/mm2) and high expressors (> than 1 immunoreactive tumour cell/mm2). There were 33 (16%) carcinomas showing both chromogranin A and secretogranin II immunoreactivity: 11 tumours (5%) were high expressors. Endocrine differentiation was not related to the disease stage, tumour location, grade, DNA ploidy and p53 protein accumulation. In the entire series chromogranin A immunoreactivity did not provide prognostic information using univariate and multivariate analysis. A worse overall survival (P = 0.048) was demonstrated for the stage III patients with high expressor tumours, but there were only five patients in this group. The results of our investigation suggest that chromogranin A immunoreactivity is not a useful variable in the prognostic assessment of colorectal adenocarcinomas.