The treatment of patients with angina pectoris is commonly evaluated according to such indexes as the frequency of anginal attacks, quantity of supplemental nitroglycerin, and exercise performance in an ergometric laboratory test. None of these indexes demonstrates the clinical change in ordinary functional limitations that may have been the major reason why a patient sought medical help. The New York Heart Association ratings of functional capacity do not refer to different types of activity and the four categories of the scale are too coarse to show distinct changes that can occur while a patient retains the same rating. A new taxonomy has been devised for rating transitions in functional capacity as noted in three different kinds of functional performance: occupation, customary activities, and sporadic activities. The ratings of change in these three activities can be combined into single global rating. When applied to conventional questionaire data for 309 patients in a randomized double-blind therapeutic trial, the new classifications showed a statistically significant superiority, in each type of functional transition and in the global ratings, for patients receiving timolol maleate rather than placebo. By augmenting the conventional information used for therapeutic evaluation, the new taxonomic indexes can expand the scientific scope of antianginal treatment. Data derived from history-taking can be just as statistically significant as "harder" forms of information, while simultaneously being more pertinent for the clinical challenge of choosing and evaluating the agents used in patient care.