THE RELATIVE EFFECTIVENESS OF EIGHT TYPES OF VISUAL ILLUSTRATION OF THE HUMAN HEART WAS TESTED IN NINTH THROUGH TWELFTH GRADE CLASSES. THE EIGHT TYPES--ABSTRACT LINE DRAWINGS, DETAILED SHADED DRAWINGS, PHOTOGRAPHS OF HEART MODELS, AND REALISTIC MODELS, EACH IN BLACK AND WHITE AND IN COLOR--AND A CONTROL PRESENTATION WITH NO ILLUSTRATIONS WERE ASSIGNED RANDOMLY TO ONE CLASS EACH PER GRADE LEVEL. EACH TREATMENT CONSISTED OF A TAPE RECORDED ORAL PRESENTATION ON THE HEART, AND 39 SLIDES WHICH WERE IDENTICAL IN SIZE AND FORMAT TO THE SLIDES IN EACH OTHER TREATMENT. EVALUATIVE DEVICES WERE A PHYSIOLOGY KNOWLEDGE PRETEST, AND FOUR CRITERION PRETESTS IN DRAWINGS, IDENTIFICATION, TERMINOLOGY, AND COMPREHENSION, WHICH WERE USED AS IMMEDIATE AND TWO-WEEK-DELAYED PRETESTS. DATA FOR THE CRITERION TESTS WERE SUBJECTED TO ANALYSIS OF COVARIANCE, AND MEANS WERE COMPARED BY DUNN'S C-PROCEDURE TO AVOID OBTAINING SPURIOUS SIGNIFICANT DIFFERENCES. IN THE IMMEDIATE POST-TESTS, THE ABSTRACT LINEAR REPRESENTATIONS WERE SUPERIOR TO MORE "REALISTIC" PRESENTATIONS, PROBABLY BECAUSE THEY ISOLATED MATERIAL TO BE LEARNED AND DID NOT PRESENT OTHER IRRELEVANT STIMULI. SIGNIFICANT DIFFERENCES EXISTED ON THE IMMEDIATE POST-TESTS, BUT ON THE DELAYED MEASUREMENT, DIFFERENTIAL EFFECTS OF THE NINE TREATMENTS DISAPPEARED FOR ALL TESTS FOR ALL FOUR GRADES, WITH ONE EXCEPTION. APPENDICES INCLUDE A BIBLIOGRAPHY, THE EVALUATION INSTRUMENTS, THE TEACHER SCRIPT, AND SAMPLE VISUAL ILLUSTRATIONS. (BB)