Orthotopic tumour models for colorectal cancer are a complementary tool for the study of tumours in vivo. They are more closely related to human cancer than are subcutaneous tumour models, since evaluation of spontaneous metastasis formation is possible. In the present study, fragments of subcutaneous xenografts established from 12 well-described and generally available colorectal cancer cell lines were implanted in the caecum of nude mice and tumour growth and metastatic events registered. The results showed considerable differences between the cell lines with respect to take rate, tumour growth and metastatic ability. This resulted in variable disease progression that seemingly reflects clinically relevant heterogeneity. The most common metastatic findings were mesenteric lymph-node metastases, occurring at variable frequency in tumour-bearing mice with 10 out of 12 cell lines, whereas only one line gave rise to liver metastases, in two of 10 animals. The study provides useful background information on the 12 colorectal cancer cell lines in a clinically relevant orthotopic tumour model.