The topic of this investigation was to compare precancerous lesions of the prostate (prostatic intraepithelial neoplasia -PIN- and atypical hyperplasia -AH-) and invasive carcinomas concerning DNA ploidy (image cytometry/ICM) and morphologically feasible chromosomal aberrations (interphase cytogenetics/NISH). The aim was to find clues to formal pathogenesis of prostatic cancer. Prostatic tissue of 76 patients (76 areas with carcinoma, 71 with PIN, and 12 with AH) was examined by means of ICM. In 44 cases of coincidental PIN and carcinoma, the gradings of PIN and carcinoma correlated. C-values, 2,5c-exceeding-rate, and aneuploidy rate turned out to increase in PIN and carcinoma with increasing grading (P < 0.01). In some of these cases NISH was carried out in serial sections by applying centromer-(X,Y,1,7,8,10,17,18) and telomer-(1p) specific DNA probes. The result of this approach was an increase in the number of chromosomal aberrations and chromosomes involved correlating with the grading. Our conclusion is that PIN 1 could be regarded as the precancerous lesion mainly to higher differentiated carcinomas, whereas PIN 2 and 3 should be considered a preneoplastic condition mainly of moderately and low differentiated carcinomas.