Mass treatment with albendazole, co-administered with another antifilarial drug, is being promoted as part of a global programme to eliminate lymphatic filariasis.To assess the effects of albendazole on patients or populations with filarial infection, and on morbidity in patients with filarial infection; and to assess the frequency of adverse events for albendazole both given singly or in combination with another antifilarial drug (diethylcarbamazine or ivermectin).We searched the Cochrane Infectious Disease Group's trial register (September 2003), the Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 3, 2003), MEDLINE (September 2003), EMBASE (September 2003), LILACS (September 2003); and checked the reference lists and contacted experts, international organizations, and a pharmaceutical company.Randomized and quasi-randomized controlled trials of albendazole singly or in combination with anti-filarial drugs in people or populations with lymphatic filariasis.Two reviewers assessed eligibility and trial methodological quality. We calculated relative risks (RR) with 95% confidence intervals (CI) for binary outcomes, and where appropriate, combined them in a meta-analysis using the fixed effect model or random effects model.Four small studies met the inclusion criteria (a total of 2473 children and adults, of whom 536 had detectable microfilariae). No effect of albendazole on microfilaraemia was demonstrated in two studies (placebo controlled, RR 0.97, 95%CI 0.87 to 1.09, n = 195). When compared to ivermectin, albendazole performed worse (RR 0.84, 95% CI 0.72 to 0.98, 2 studies of patients initially microfilariae positive, n = 198). When compared to diethylcarbamazine, no statistically significant difference was detected, but numbers were small (n = 56). Two studies compared albendazole plus ivermectin to ivermectin alone on the presence of microfilaraemia. Results were mixed: one study showed the combination to be more effective (RR 0.27, 95% CI 0.11 to 0.70, n = 52), but the other did not demonstrate a statistically significant difference (RR 1.04, 95% CI 0.87 to 1.25, n = 145). A further study compared albendazole plus diethylcarbamazine to diethylcarbamazine alone and did not demonstrate a difference on microfilaraemia prevalence (RR 1.57, 95% CI 0.44 to 5.60, n=35). No study examined the effects of the drugs on adult worms.There is insufficient reliable research to confirm or refute whether albendazole alone, or co-administered with diethylcarbamazine or ivermectin, has an effect on lymphatic filariasis.