Two-hundred-fifty CHD cases and 500 matched controls from the Western Collaborative Group Study were studied to assess the 8.5-yr prospective relationship of specific behavioral dimensions to the incidence of coronary heart disease. Type A structured interviews administered at intake were reevaluated in terms of 12 operationally defined components, which include previously described facets of the Type A behavior pattern. Univariate risk analyses using the matched logistic model found hostility (RR = 1.92, p less than 0.001), speaking rate (RR = 1.66, p = 0.003), immediateness (RR = 1.62, p = 0.009), competitiveness (RR = 1.50, p = 0.013), and Type A content (RR = 1.38, p = 0.045) to be significantly related to CHD incidence. Of these, only hostility remained a significant risk factor (RR = 1.93, p less than 0.001) when all 12 components were included in the model. The original Type A global ratings and traditional CHD risk factors were also analyzed in conjunction with the components. The Type A behavior pattern comprises both benign and coronary-prone facets, with the latter most exemplified by hostility.