Nuclear mitotic apparatus protein (NuMA) is a 239 kDa internal nuclear matrix protein described to be elevated in cancer patients, especially in colorectal carcinoma and early colorectal cancers. We tested the significance of NuMA as tumour marker in colorectal cancer and also the sensitivity/specificity profile in general. Therefore, we investigated in a retrospective clinical study 507 sera from patients suffering from solid tumours, with the main emphasis on colorectal carcinoma, and 418 sera from patients with benign diseases and healthy individuals. Testing was done with a double monoclonal enzyme immunoassay detecting head and rod domain of NuMA and results were compared to the established tumour associated antigens. Based on a specificity of 95% versus the benign reference group of gastrointestinal diseases, we found--at the time of primary diagnosis--a sensitivity for colorectal cancer of 8% for NuMA, 36% for CEA and 17% for CA 19-9. Regarding T-stages of colorectal cancer no marker detected T1 when regarding 95% specificity-cut-off value but NuMA showed little more sensitivity when based on a 95% specificity cut off value versus healthy. This could not be shown in Dukes' stages. Regarding all other solid tumours tested--all based on a specificity of 95% for the corresponding benign reference groups--no advantage of NuMA in sensitivity for all other solid tumours investigated was found. No additional sensitivity could be observed. Based on our results, the NuMA-assay in its present form has no clinical relevance.