High levels of adherence in clinical trials are essential for producing accurate intervention efficacy estimates. Adherence to clinical trial products and procedures is dependent on the motivations that drive participants. Data are presented to document reasons for trial participation and adherence to daily aciclovir for HSV-2 and HIV-1 genital shedding suppression among 300 HIV-1/HSV-2 seropositive women in South Africa. In-depth interviews after exit from the trial with 31 randomly selected women stratified by age and time since HIV diagnosis confirmed high levels of adherence measured during the trial. Main reasons for trial participation were related to seeking high-quality health care, which explains high levels of adherence in both study arms. Concerns that women would abuse reimbursements, fabricate data, and share or dump pills were not corroborated. Altruism is not a primary motivator in these settings where access to quality services is an issue. This study provides further evidence that good adherence of daily medication is possible in developing countries, particularly where study activities resonate with participants or fill an unmet need.