Tumour DNA samples of 20 patients with colorectal carcinoma were tested for c-myc amplification, using a quantitative dot-blot hybridization. Statistical analysis involving clinical and histological parameters like degree of differentiation, Dukes' stage, TNM staging system, age, sex and severity of disease, was applied to estimate the prognostic value of c-myc amplification. The amplification of the investigated oncogene--1.61-fold on the average--was found to significantly correlate with the presence of distant metastasis (corr. coeff.: 0.506, P < 0.05) and the severe course of the disease (corr. coeff.: 0.468, P < 0.05). This result supports the hypothesis that tumour cells with c-myc amplification represent a more malignant and aggressive phenotype. It is also worth noting that both c-myc amplification and formation of distant metastasis are late events in the progression of colorectal cancer, which accounts for the more severe course of the disease.