This study investigated the use of multimedia materials to enhance student learning in a large, introductory biology course. Two sections of this course were taught by the same instructor in the same semester. In one section, video podcasts or "vodcasts" were created which combined custom animation and video segments with music and faculty voiceover, and which were designed to address those topics known to be difficult for biology students. In the other section, "class captures" were produced for each class session which combined the output of the classroom's digital projector with a recording of the instructor's voice. Both types of multimedia were made available to students online through the Blackboard-Vista course management system. Student reception of the custom vodcasts was more enthusiastic than reception of the class captures. Additionally, after controlling for potential confounding variables including students' overall GPA, major, sex, ethnic background, high school rank, year in school, composite ACT scores, and initial level of evolution knowledge, it was found that students who used the custom vodcasts achieved significantly higher scores (9.4%, or 2/3 of a standard deviation) on an end-of-term test of evolution knowledge than students who used the class captures. Students in the two sections of the class achieved statistically equivalent final grades in the course, however. It is argued that vodcasts are a more effective way of utilizing multimedia in large classes than class captures due to their targeting of known student problems in the course material and to their better implementation of established principles for the design of effective multimedia resources. (Contains 5 tables and 1 footnote.)