The sample covered 12 States, and selection criteria required that subjects had raped at least 10 times. The 41 rapists included 35 white males, 5 black males, and 1 Hispanic male. Ages ranged from 23 to 55 years. of the 41 men, 15 were participating in some form of sex offender treatment at the time of interview. Change over time was examined for the amount of force used by rapists, the amount of pleasure experienced, whether victims resisted assault, and assault duration. Collectively, the sample was responsible for 837 rapes, more than 400 attempted rapes, and over 5,000 'nuisance' sexual offenses. Results showed that, while the amount of forced used by rapists did not change from first to last rape overall, there were 10 individuals for whom the amount of force increased from first to last rape. Data also indicated that, when victims resisted, the amount of pleasure experienced by rapists was greater and rape duration was longer. The majority of serial rapists consistently used only minimal force and inflicted only minimal injury on their victims. However, about 25 percent of the respondents raped significantly more victims, escalated in the amount of force used, and inflicted moderate to fatal injuries by the end of their 'rape careers.' 17 references, 2 tables. (Author abstract modified)