Incidence rates of invasive prostate cancer vary markedly among countries of the Pacific Basin, and migrant studies have shown that this is at least partly due to environmental factors. Future epidemiology studies in these countries should be conducted so that this variability in incidence can be explained. Prevalence ratios of latent prostate carcinomas of the infiltrative type vary with incidence rates of invasive carcinomas, and a collaborative case-control study of infiltrative and noninfiltrative latent carcinomas in the Pacific Basin, combined with a standardized pathological review of specimens obtained at autopsy, could provide new etiological clues. Factors that should be investigated include fertility and sexual practices; exposure to zinc, cadmium, and mercury compounds; prior benign prostatic hypertrophy; diet; conditions that may alter endogenous levels of androgens and estrogens; and family history of diseases of the prostate. Events during the fourth decade of life may be of particular importance. Case-control studies of invasive prostate cancer in high- and low-risk populations are currently being conducted, and additional ones are not warranted until results from these are available. Investigators should use these results in planning the proposed study of latent prostate carcinoma.