Context and setting Didactic lectures are traditional in medicine. They are intended to impart information on problematic topics and introduce difficult concepts. However, the type of sustained low-level activity that occurs in lectures does not promote effective learning or retention of knowledge; indeed it has been shown that attention wanes after about 15–20 minutes and knowledge recall following didactic teaching often amounts to only about 20% of the material presented. Thus, knowledge retention following conventional teaching often decays at an undesirable rate. Why the idea was necessary The use of audience response systems (ARSs) has been suggested to improve and facilitate learning in a didactic lecture setting by increasing student participation, giving instant feedback, and improving knowledge retention. What was done We used an ARS in a phase 1 medical programme to assess prior knowledge, understanding and information decay in Year 1 medical students. A total of 93 undergraduate medical students attended physiology lectures incorporating the use of the ARS KEEpad. KEEpad was used to ask the students a multiple-choice question (MCQ) before the lecture to assess prior knowledge of some aspects of renal physiology, at the end of the lecture to assess understanding and thus whether learning had occurred, and 5 weeks later to assess knowledge retention. Ethical permission was not required as the data represent part of anonymised, routinely collected data, the collection of which cannot harm. At the end of the module, students were asked to complete an evaluation form which included two questions on the use of KEEpad. The form used a 6-point Likert scale with the descriptors on an even scale and allowed space for free text comments. The two items regarding use of the ARS were: ‘The KEEpad audience response system gives me feedback on my progress’ and ‘The KEEpad audience response system supports the learning experience.’ Evaluation of results and impact Before the lecture was delivered, 40% of the class selected the correct answer using KEEpad, showing a moderate degree of prior knowledge of this topic. This was expected as the students had been introduced to the concept of Starling forces in cardiovascular physiology and thus were demonstrating an ability to apply the knowledge to a different body system. At this point the correct answer was not given. The same question was then asked at the end of the lecture and the percentage of students who chose the correct answer increased to 79%. Five weeks later, the same question was put to the students, again using KEEpad. The percentage of students selecting the correct answer was 60%. This represents a 77% recall rate, considerably higher than rates suggested by the literature following conventional didactic lectures. The evaluation forms showed student levels of satisfaction regarding use of KEEpad were 100% and 98%, respectively. The use of KEEpad demonstrated that learning occurred during the didactic lecture and that the recall rate after 5 weeks was high. Students’ satisfaction with the use of KEEpad for feedback and the learning experience during lectures was extremely high. The ARS is a useful and low-cost tool with which to improve knowledge retention in undergraduate medical education.