The cell-cycle inhibitor p27(kip1) is a potential tumor suppressor and might serve as a prognostic marker in rectal cancer, in particular with regard to patient selection for adjuvant therapy.Immunohistochemical analysis was performed, using an anti-p27(kip1) monoclonal antibody, on paraffin sections of two matched [age, gender, UICC stage, year of operation (1982-1991)] groups of patients (n = 2 x 82) with rectal carcinoma curatively treated by surgery alone. The groups differed only in subsequent metachronous distant metastatic spread. All patients had to meet the selection criterion "free of local disease," in order to exclude surgical influence. Follow-up was prospective (median of 74 months). The intensity of staining (-, +, ++, ) and rate of positive cells (as a percentage of total tumor volume) were judged separately for cytoplasms and nuclei.On multivariate analysis, cytoplasmic staining intensity proved to be the best prognostic factor of disease-free survival and approached statistical significance (P = 0.0552, Cox regression). On univariate analysis, considering cytoplasmic staining alone, intensely stained ( ) tumors showed significantly poorer disease-free survival (vs ++, +, -; Kaplan-Meier, logrank, P = 0.0185).The demonstrated correlation between cytoplasmic compartmentalization of p27(kip1) and increased metastatic spread as well as disease-free survival underscores the role of p27(kip1) in rectal cancer. However, since other reports emphasize the importance of nuclear p27(kip1) expression, the mechanisms of steady-state and subcellular distribution of p27(kip1) remain unclear, and further investigation is needed.