We have used data from a probability sample of African-American and Hispanic youth living in low-income urban household to describe their heterosexual experiences and the influence of relationships with different kinds of sexual partners (married/lived with, well known, casual) on types of intercourse (oral, anal, vaginal), condom use, and use of other birth control methods. The Generalized Estimating Equation method for data sets with multiple observations on the same subject was used to examine whether an individual's behavior differs with different kinds of partners and how behavior with a given partner is affected by experience with other relationships. Results indicate that (a) with the exception of African-American men, sexual and contraceptive behavior varied considerably with different kinds of partners; (b) heterosexual oral and anal intercourse is more common among Hispanic than African- American youth; and (c) regardless of experience with other relationships, consistent condom use as well as use of any type of contraceptive method tend to be less likely with a casual sex partner. Data regarding percentages of consistent condom use (20%-45%) and increased involvement in risky behavior associated with multiple partners further emphasize the need for interventions that enhance condom use and discourage involvement with multiple partners.