A comparison was made of hypermedia learning environments and traditional instruction in terms of contribution to declarative, procedural, and conditional knowledge acquisition and retention in a specific subject area through a pretest-posttest control-group design. Thirty-nine 9th-grade biology students were assigned to experimental (hypermedia learning environment) and control (traditional instruction) groups through a matched-pair technique. Both groups were given pre-, post-, and retention tests. Posttest results indicated no significant difference between control and experimental groups in acquisition of declarative, conditional, and procedural knowledge. However, retention test results showed that the experimental group retained all three types of knowledge significantly better than did the control group.