Bioscience undergraduates, enrolled on a first-year microbiology module, participated in the introduction of peer-assisted learning (PAL) into the curriculum. The class of 122 students was divided into groups of six to ten, with one volunteer from each group assuming the role of group leader (peer tutor). Group leaders attended a compulsory training session at which they were guided through the tutorial they would lead with their peer group. The primary aim of PAL was to raise students' self-confidence in their problem-solving and numerical skills. Students were provided with the opportunity to practise problem-solving questions from past examination papers and to discuss with their peers their answers and any difficulties they encountered, particularly with regard to any mathematics involved. Students' perceptions of their PAL experience, their group leader's contribution and the training provided for group leaders were evaluated using a questionnaire. The latter revealed that bioscience undergraduates found PAL a highly valuable learning experience. In particular, they found the less formal, comfortable and relaxed atmosphere of the PAL session provided them with greater freedom to ask questions and exerted less pressure on them to answer questions correctly than a more formal staff-led session, as well as assisting them to understand the topics covered. (Contains 2 figures and 6 tables.)