An entertainment-education radio soap opera introduced in Tanzania in 1993 was evaluated by means of afield experimental design in which the radio program was broadcast by seven mainland stations of Radio Tanzania. An eighth station broadcast alternative programming from 1993 to 1995, its listenership serving as a comparison area in which contemporaneous changes in family planning adoption were measured. The soap opera was subsequently broadcast nationwide from 1995 to 1997. Data about the effects of the radio soap opera were gathered in five annual surveys of about 2,750 households in the comparison and the treatment areas and from a sample of new family planning adopters in 79 health clinics. The soap opera had strong behavioral effects on family planning adoption; it increased listeners' self-efficacy regarding family planning adoption and influenced listeners to talk with their spouses and peers about contraception.