The purpose of this experiment was to compare an inquiry-oriented Biological Sciences Curriculum Study (BSCS) style laboratory approach with a more directive traditional approach on student outcomes in the cognitive and affective domains of learning at two private, midwestern liberal arts colleges. Intact laboratory sections of students enrolled in introductory general biology were randomly selected into two treatment groups. Pretest and posttest measures were taken on three dependent variables: (1) biological content achievement; (2) reasoning ability; and (3) attitude toward biology. The experimental group using the BSCS-style laboratory approach scored significantly higher than the comparison group in levels of performance on biology content achievement. There were no significant differences between the two groups in performance levels on attitude toward biology or on reasoning ability. However, both groups experienced an increase in the number of formal thinkers as indicated by pretest-posttest gain scores on the reasoning ability test. These results lend support to the hypothesis that a BSCS-style laboratory approach fosters desired learner outcomes at the postsecondary level. In addition, these findings support the notion that the science laboratory may be used as a primary vehicle to promote formal reasoning skills. (Author/CW)