The concepts of efficacy and effectiveness are examined from the viewpoints of the traditions and philosophies of health-care research and social program evaluation. Consideration of the status of the program being assessed, its availability to, and its acceptance by the target audience leads to the derivation of four levels of health promotion program testing: efficacy trials, under optimum conditions of program implementation and recipient participation; treatment effectiveness trials, with expected variation in target audience acceptance; implementation effectiveness trials, under varying conditions of implementation; and program evaluation of previously untested programs. These four levels of testing, together with experience in one area of health promotion research (smoking prevention), suggest eight phases of research for the development of health promotion programs: basic research, hypothesis development, pilot applied research, prototype evaluation studies, efficacy trials, treatment effectiveness trials, implementation effectiveness trials, and demonstration evaluations. Issues of design, the use of random assignment, the use of blinding procedures, and of the role of process evaluation in these different research levels, particularly efficacy and effectiveness trials, are considered in light of the terminologies and methods of health-care and social program evaluation research. Suggestions are made for improved health promotion research.