Two related studies were performed aimed at finding if and how prior knowledge of threat and efficacy information in a fear appeal message is associated with message outcomes (attitude and behavioural intentions). the extended Parallel Process model (ePPm) (Witte 1992; 1998) served as theoretical framework for one study about a chlamydia fear appeal (n = 57) and another about an alcohol abuse fear appeal (n = 59). Findings from both studies suggest that prior knowledge of threat information is hardly relevant for readers’ reactions to a fear appeal message. Prior knowledge of efficacy information, however, proved to play a more important role, most often in a positive way. Findings from both studies furthermore suggest that the ePPm may be incorrect in assuming that individual differences – in this case, in prior knowledge – may only affect fear appeal outcomes in an indirect way, that is through different perceptions of threat and efficacy.