THE EFFECT ON ACHIEVEMENT OF INTEGRATING THE STUDIES OF SPANISH AND BIOLOGY WAS REPORTED. STUDENTS IN THE EXPERIMENT RECEIVED INSTRUCTION IN BIOLOGY THROUGH DISCUSSIONS AND READINGS IN SPANISH. THE SPANISH LANGUAGE THUS BECAME THE MEANS TO AN END RATHER THAN THE SOLE END ITSELF. EXPERIMENTAL MATERIALS WERE SELECTED AND DEVELOPED, CONSISTING OF FILMS, DIALOGS, TESTS, TAPES, VISUAL AIDS, A TEACHING MANUAL, AND STUDENT TEXTS. THE EXPERIMENT WAS CONDUCTED WITH ELEMENTARY AND SECONDARY STUDENTS. CONTROL GROUPS WERE USED FOR COMPARATIVE PURPOSES. EVALUATIONS OVER A PERIOD OF ABOUT 1 SEMESTER SHOWED NO SIGNIFICANT DIFFERENCES BETWEEN EXPERIMENTAL AND CONTROL GROUPS IN SCHOLASTIC ACHIEVEMENT. AN UNBIASED INSTRUMENT FOR EVALUATING STUDENT ACHIEVEMENT COULD NOT BE FOUND. DIFFERENCES IN STUDENT ENTHUSIASM APPEARED TO FAVOR EXPERIMENTAL TREATMENTS. (RS)