By examining data on 250,109 cases of prostate cancer from the National Cancer Institute SEER Program from the years 1973 - 1994, these investigators were able to detect grade, stage, and age differences between the pre-prostate specific antigen (PSA) test period (1973 - 1983) and the post-PSA era (1989 - 1994). They found that during pre-PSA period, the higher and lower graded cancers (known Gleason scores) had roughly the same incidence at 17 to 23 cases per 100,000 men. Yet, after the start of the PSA era, there was a major increase in incidence to 97.4 cases per 100,000 men. About 75% of the increase was accounted for by moderately differentiated tumors. Only 8% of the increase was the result of newly diagnosed well- differentiated prostate cancers. Also, distant stage rates for the disease declined by 50% from the pre-PSA era (from 14.6 to 7.1 cases per 100,000 men). After examining age data, they found the average age at diagnosis declined slightly from 72 (pre-PSA), to just under 69-1/2 during th e PSA era. The investigators suggest that declining age at diagnosis and decreasing distant stage rates suggest earlier diagnosis takes place during the PSA era. However, the definitive impact of these effects on patient outcome must await future mortality data.