Warnings provide important information about the hazards that are faced in a variety of circumstances. However, this information may be supplemented extensively by previous experiences and by the environmental circumstances in which the warning is presented. Two experiments evaluated the effect of prior experience and observation of others on perception of risk. One experiment examined perception of risk for the same signs under different circumstances. The second experiment evaluated the degree of seriousness the participants thought implied by warnings as a function of presence or absence of requests for compliance. Although no dependable difference was found in a preliminary test of perception of risk, later ratings of changes in concern for the seriousness of the hazards showed differences as a function of the requirement for compliance. The results were discussed in terms of the importance of reinforcement of warnings by behavior modeling and by physical barriers. Relevance to industry Industrial settings involve many circumstances in which unsafe behavior may be exhibited and may consequently lead others to perform unsafe acts. Some of the factors that may influence such behaviors are the insistence on complying with safe procedures and making unsafe acts more difficult to perform.