The primary aim of this report was to examine the significance of increased DNA sequence copy number (gene amplification) in human prostate cancers. Three methodologies (chromosome microdissection, comparative genomic hybridization, and fluorescence in situ hybridization) were combined to (a) identify a common region of gene amplification in human prostate cells and (b) evaluate in patient samples the prevalence of this genetic change in both primary and recurrent prostate samples. The results of chromosome microdissection revealed a common amplified band region (8q24.1-24. 2) in two prostate cases with cytological evidence of gene amplification (double minutes). Fluorescence in situ hybridization using the 8q microdissection probe was performed on fresh tumor touch preparations from 44 randomly selected prostatectomy specimens. Amplification of DNA sequences from 8q24 was observed in 4 (9%) of 44 cases. Four of the 44 patients in this series presented with a positive lymph node at initial diagnosis and 3 of these 4 patients showed 8q amplification. Because of this finding, comparative genomic hybridization and fluorescence in situ hybridization were performed on tumor cells from nine prostate cancer patients with recurrent disease. In eight of nine cases a gain of DNA sequences encompassing 8q24 was observed. Taken together with other evidence implicating 8q gain in prostate cancer progression, these results suggest that the analysis of this genetic change may have diagnostic utility as a marker of prostate cancer progression.