Controlled human infection model studies, or challenge studies, involve the intentional infection of a consenting healthy human volunteer with a virulent organism under controlled conditions Such studies differ from clinical trials in that though both involve healthy volunteers, in challenge studies the potential harm experienced by participants is intended, not merely potentially foreseen, as in clinical trials. Given the special nature of CHIM studies, careful consideration of participant selection and compensation is essential. This paper explores the ethical criteria for recruiting participants in such studies, their own possible motivation such as monetary payment or access to treatment and how that should not be an inducement. It also distinguishes between compensation as inducement and fair compensation for the possible contracting of an illness, isolation and adverse effects, and indicates that more research on the subject needs to be done