The Biology Intensive Orientation for Students (BIOS) Program was designed to assess the impact of a 5-d intensive prefreshman program on success and retention of biological science majors at Louisiana State University. The 2005 pilot program combined content lectures and examinations for BIOL 1201, Introductory Biology for Science Majors, as well as learning styles assessments and informational sessions to provide the students with a preview of the requirements of biology and the pace of college. Students were tracked after their BIOS participation, and their progress was compared with a control group composed of students on the BIOS waiting list and a group of BIOL 1201 students who were identified as the academic matches to the BIOS participants (high school GPA, ACT score, and gender). The BIOS participants performed significantly better on the first and second exams, they had a higher course average, and they had a higher final grade than the control group. These students also had higher success rates (grade of "A," "B," or "C") during both the fall and spring semesters and remained on track through the first semester of their sophomore year to graduate in 4 yr at a significantly higher rate than the control group. (Contains 1 table and 4 figures.)