To assess the prognostic value of CD44s and CD44v6 tumour expression for patients with T1-T2 conventional renal cell carcinomas, a retrospective immunohistochemical analysis of 95 patients was undertaken. These patients had undergone a radical nephrectomy, performed in three institutions in France between 1987 and 1993. The mean age of the patients was 62.9+/-10.2 years (range from 37 to 85 years) with 66.3% males. At the time of surgery, 84 patients had a T1 and 11 a T2 renal tumour. Fuhrman nuclear grading showed 44 (46.3%) tumours of grade 1, 39 (41.1%) of grade 2, and 12 (12.6%) of grade 3. The mean follow-up period was 58.1+/-36.1 months. At the end of follow-up, eight patients (8.4%) had metastatic disease and no local recurrence was seen. Immunohistochemistry showed that 26 tumours (27.4%) expressed CD44s, but none expressed CD44v6. Statistical analysis showed that CD44s expression was correlated with tumour size (p=0.006) and Fuhrman grading (p<10(-4)). Among the various parameters tested for the multivariate analysis, CD44s expression correlated only with disease-free survival (p=0.04). It is concluded that CD44s expression, but not CD44v6, is of potential prognostic interest in patients with localized T1-T2 conventional renal cell carcinomas.