As there is a growing interest in experienced workers mentoring co-workers in workplace settings, it is necessary to understand its impact on those who are nominated as mentors. Here, data from eight mentors who participated in a year-long trial of guided learning in a workplace are used to illuminate the demands upon and benefits for workplace mentors. In the study all mentors noted the efficacy of guiding learning in the workplace. However, guiding the learning of others made considerable demands on these individuals. Finding time for mentoring and the low level of support by management were reported as making the mentors' work intense. Moreover, although workplace mentoring was found to have the capacities to improve learning, much of that improvement was centred on the mentors' actions and energies. For some mentors, it was a worthwhile and enriching experience. For others, the demands were not adequately offset by benefits that they experience in assisting co-workers to learn.