Acidic fibroblast growth factor is a regulatory peptide involved in cell proliferation, differentiation and motility. We used a polyclonal antiserum raised against purified native bovine acidic fibroblast growth factor, with no cross-reactivity for basic fibroblast growth factor to detect acidic fibroblast growth factor in tissue extracts and urine samples by means of a competitive enzyme immunoassay. Histochemical analysis was also performed on 10 specimens of normal urothelium and 50 of bladder cancer. Acidic fibroblast growth factor immunoreactive material was found in normal urothelium (1.77 +/- 2 ng./gm. tissue) and was increased more than 10-fold in patients with transitional cell carcinoma of the bladder (20.36 +/- 12 ng./gm. tissue). Immunohistochemical analysis localized immunoreactivity in the epithelial compartment of bladder tumors. Acidic fibroblast growth factor was assayed in urine from 579 individuals comprising a control group (114) and patients with benign prostatic hypertrophy (133), carcinoma of the prostate (96) or transitional cell carcinoma of the bladder (236). There was a significant difference in the frequency of urinary acidic fibroblast growth factor detection among the patients with invasive transitional cell carcinoma, the control group (p < 0.001) and the patients with prostatic disease (p < 0.01). The sensitivity was 72% and the specificity was 91%. Furthermore, the frequency of acidic fibroblast growth factor detection by enzyme immunoassay in the urine and the intensity of immunostaining was correlated with the stage of the disease. These data strongly suggest that acidic fibroblast growth factor is a potential marker for bladder tumors that may be of use in the noninvasive followup of patients with bladder cancer. We present a simple and reliable enzyme immunoassay for the detection of acidic fibroblast growth factor in voided urine that might be useful to quantitate this marker.