We examined the process of informed consent in an antiretroviral trial in Nigeria. A semi-structured questionnaire was administered to 88 out of 180 people enrolled in the trial. This covered all aspects of the information disclosed in the leaflet of the antiretroviral trial. We found that 75 (85 per cent) of the respondents knew that the purpose of the research was to test a new drug and 13 (14 per cent) believed that they were receiving free treatment for HIV. Participants understood certain aspects of the research, especially the benefits and duration. Their understanding of the trial's risks and their right to refuse to participate and to withdraw was low. Their level of understanding was significantly related to age but not to gender, marriage, education, religion, employment and occupation. Signed informed consent is not a guarantee that participants have understood the information given to them and therefore made a voluntary decision to participate. Researchers should make sure that the process of obtaining informed consent achieves the desired outcome. This is especially important in the developing world where access to health care is limited, potential participants are poor and literacy levels are low.