The cellular DNA content was quantitatively and the expression of oncogene ras P 21 qualitatively assessed in paraffin embedded tumor specimens from 62 patients with bladder tumors, using the paraffin-embedded bladder mucosa specimens from 7 patients with non-neoplastic urinary diseases as control. The results were retrospectively analysed in relation to the outcome of patients on follow-up. In 25 cases with superficial bladder tumor the positive rate of P 21 expression and the frequency of aneuploid were 92% and 12%, respectively. But in 37 cases with infiltrative bladder tumor the positive rate of P 21 expression and the frequency of aneuploid were 29.7% and 78.3%, respectively. It was considered that the P 21 expression may imply early bladder tumor whereas the finding of aneuploid was a parameter of advanced bladder tumor. Our results also showed that the expression or non-expression of P 21 was closely related to DNA ploid patterns. The positive rate of P 21 expression was 90% in the diploid bladder tumors and 50% in the tetraploid bladder tumors. The P 21 expression was negative in all the cases with double aneuploid bladder tumors. The results suggest that DNA ploid patterns and P 21 expression, when analyzed simultaneously, would be prognostically more informative than either alone.