In this study we investigated 56 renal cell carcinomas immunohistochemically for the expression of proliferating cell nuclear antigen (PCNA) and tumour suppressor protein p53. We also analyzed for the presence of human papilloma virus (HPV) DNA subtypes 6, 11, 16, 18, 31 and 33 by in situ hybridization. In carcinomas which showed more than 10% of PCNA positive nuclei there were significantly more cases with invasion (P = 0.032) or metastatic disease (P = 0.047). Nine out of 22 grade III-IV tumours (40.9%) but only six out of 30 grade I-II tumours (20%) showed more than 10% of PCNA positive cells (P = 0.097). Patients with 10% or more PCNA positive cells in kidney tumours had more advanced disease at the time of diagnosis than those showing less PCNA positive cells (P = 0.05). Six p53 positive cases were found among 56 tumours (11%), but only one case had more than 10% positive cell nuclei. The presence of HPV DNA was found in 29 out of 56 cases (52%). Multiple subtypes were found in 19 cases (34%). The most commonly occurring subtypes were 18 and 33. There was no association between PCNA, p53 and the presence of HPV DNA subtypes. Because of the association of PCNA with invasion and metastatic disease, it would be worth while to study PCNA further as a possible marker for aggressiveness of renal carcinomas. Both this study and those concentrated on mutational analysis suggest that p53 is generally not important for the development of renal cell carcinoma. On the other hand, the presence of HPV DNA in these tumours implicates HPV viral infection in the aetiology of renal cancer.