The impact of introducing computer-based self-assessment quizzes on examination performance was monitored in 5 modules delivered to undergraduate students in the first, second, and final years at university over a 2-3 year period. The patterns of usage were also monitored to determine the extent to which the quizzes were used and whether there were differences between the students at different stages of their education. Overall, all groups used the CBA package in broadly similar ways, although year 1 students were least likely to access their quiz. Most students used the quizzes during normal 'office hours' between Monday and Friday, but up to 22% of use occurred in the evenings and 3-20% at weekends. Most log-on events were recorded in the weeks immediately prior to an examination. There was a positive relationship between the introduction of the quizzes and mean examination mark; in particular, increases in the proportion of students obtaining good (>60%) marks were observed.The results suggest that the provision of computer-based self-assessment quizzes is helpful to students and that the opportunity to access them at any time is appreciated. At present, it appears that the more motivated individuals are assisted most by the quizzes. Integration of formative CBA into a programme of learning appears to be beneficial, particularly when used in conjunction with other forms of formative assessment.