OBJECTIVE: To review the recent literature on the approved uses of enoxaparin, dalteparin, ardeparin, and tinzaparin and the evidence for therapeutic equivalence. DATA SOURCES: A MEDLINE search (1993–January 2001) was conducted to identify English-language literature available on enoxaparin, dalteparin, ardeparin, and tinzaparin. STUDY SELECTION: All controlled trials evaluating low-molecular-weight heparins (LMWHs) versus standard therapy powered to detect a significant difference were reviewed. DATA EXTRACTION: Agents were reviewed with regard to safety and efficacy. DATA SYNTHESIS: As a class, LMWHs have chemical, physical, and clinical similarities. LMWHs have greater bioavailability, longer half-lives, a more predictable pharmacologic response, possible improved safety, and similar or greater efficacy compared with unfractionated heparin (UFH). Because of this, enoxaparin, dalteparin, ardeparin, and tinzaparin are being considered as alternatives to UFH or warfarin, and there is potential for therapeutic interchange. Evaluation of clinical trials is limited because of differing diagnostic methods, drug administration times, dose equivalencies, and outcome measurements. CONCLUSIONS: Only 1 trial has evaluated 2 LMWHs in a direct comparison in the same study. There is insufficient evidence for determining the therapeutic equivalence of LMWHs.