Experimental, epidemiologic, and clinical trial data indicate the antineoplastic effects of calcium and vitamin D in large-bowel neoplasia. The aim of this study was to determine serum levels of vitamin D metabolites and parathormone (PTH) in patients with colorectal cancer (CRC) and to extract conclusions comparing their different levels in serum with healthy individuals. Group 1 (cancer patients) was consisted of 140 patients with CRC with clinical stages Duke's A: 12, B: 52, C: 62, and D: 14. Serum levels of 25(OH)D(3), 1,25(OH)(2)D(3), and PTH were determined in all patients. The findings are: (a) No significant difference was found in the serum levels of 25(OH)D(3) in each Duke's clinical stage in cancer patients, (b) serum 1,25(OH)(2)D(3) levels decreased with advanced cancer stages, and (c) serum levels of PTH showed a corresponding increase. Low serum levels of 1,25(OH)(2)D(3) on one hand and increased levels of PTH in patients with CRC on the other might be strongly related to the carcinogenetic process.