This study was conducted to analyze risk factors for dyspermia in infertile subjects in a population of men attending outpatient services for infertility in Milan, Northern Italy. Between September 1989 and November 1990 we conducted a case-control study on risk factors for dyspermia. Cases included infertile men with a diagnosis of unexplained dyspermia consecutively observed for the first time during the study period at the Outpatient Service for Infertility of the First Obstetric and Gynecologic Clinic of the University of Milan. Specific work-up was done to exclude the major known or potential causes of dyspermia and infertility in patients and their partners. Two control groups were selected. The first included normospermic men of infertile couples with negative work-up for any disease that might affect fertility, observed in the same outpatient service where cases had been identified. The second control group included fertile men of unknown semen quality who were the partners of women who gave birth at term (> 37 w gestation) to health infants in randomly selected days at the same clinic. In comparison with those who have never smoked, current smokers were at increased risk of dyspermia versus both normospermic men of infertile couples and fertile men of unknown semen quality, and the risk increased with number of cigarettes smoked per day and duration of smoking. The risk of dyspermia increased with the number of cups of coffee drunk per day compared with men drinking no or one cup per day. Likewise, alcohol drinkers were at increased risk and the risk increased with number of drinks/d.(ABSTRACT TRUNCATED AT 250 WORDS)