The tumour-suppressing gene p53 may undergo mutation by a variety of mechanisms, thus losing its tumour-suppressing activity, and ultimately behaving like an oncogene. The PAb 1801 monoclonal antibody is known to recognise both wild type and mutated p53, although in practice it seems to show a higher reactivity with the mutated gene product in several human tumours. We studied p53 overexpression in a series of 36 human tumours (17 mammary ductal infiltrating carcinomas, 11 endometrial carcinomas and 8 uterine cervical carcinomas) by means of immunohistochemistry using the PAb 1801 antibody and the streptavidin-biotin peroxidase technique. Furthermore, all tumours were screened for mutations in the "hot spot" regions of the p53 gene (exons 5 to 8) by means of SSCP (single strand conformation polymorphism) DNA analysis following amplification of the target exons using the polymerase chain reaction. A good correlation (75-100%) between positive immunohistochemistry and p53 mutations was observed in mammary and endometrial cancer, whereas mutations were detected in only two out of seven immunoreactive cervical carcinomas. Following these results, immunohistochemistry with the PAb monoclonal antibody may be safely used as a screening tool for the detection of mutated p53 in clinical samples of mammary and endometrial cancer, whereas it should be complemented with DNA analysis in cervix carcinoma.