Knowledge transfer is a key goal of learning, which this study aimed to investigate using an online training exercise for chest X-ray diagnosis. Junior medical students were trained to recognise the features of chest X-ray conditions and asked to provide diagnoses on these images and other unseen images to test for knowledge transfer. Transfer was observed but trained-for cases were diagnosed faster and more accurately. This study demonstrates that it is possible to promote knowledge transfer in junior medical students, using an online training exercise involving chest X-rays diagnosis, and is one of the few studies providing evidence of knowledge transfer in general.