The effects of components of the Health Belief Model and optimism on preventive intention were examined in 144 Hong Kong Chinese. Two variables related to the Health Belief Model, susceptibility and severity, were experimentally manipulated for an imaginary flu outbreak and a hypothetical vaccine. Participants indicated their intention to take the hypothetical vaccine after reading each of the 4 combinations of high versus low susceptibility and severity. Analysis suggested that both higher susceptibility and higher severity were associated with stronger behavioral intention to take the vaccine. Higher optimism scores were significantly associated with lower intention to take preventive action. In addition, a significant interaction was observed for optimism and severity. The effect of optimism was higher when severity was low than when it was high. Implications of these findings for research among Chinese were discussed. Copyright © 2000 Psychological Reports.