Filarial lymphedema is complicated by frequent episodes of dermatolymphangioadenitis (DLA). It is not certain whether DLA is of filarial or bacterial etiology. The frequency of episodic DLA does not depend on the presence or absence of microfilariae. Antibiotic therapy is effective in prevention and treatment of DLA. These observations point to the bacterial rather than filarial etiology of DLA. Skin and lymph node biopsies, tissue fluid, lymph, and blood from patients with chronic filarial lymphedema, and during acute episodes of DLA, were cultured for detection of bacteria. A high prevalence of bacterial isolates from the tissue fluid (64%), lymph (75%), and inguinal lymph nodes (66%) of limbs with filarial lymphedema was found. Bacillus cereus, Staphylococcus epidermidis, S. hominis, S. capitis, S. xylosus, and Micrococcus spp. were the most common isolates. Bacteria were also isolated from the blood of patients with recent episodes of DLA, with strains of the same phenotype and antibiotic sensitivity in all specimens from patients with DLA. Bacterial strains of the same phenotype and antibiotic sensitivity were documented on the toe web surface and in tissue fluid (25%), lymph (26%), or lymph nodes (41%). Increasing prevalence of bacterial isolates in tissue fluid, lymph, and lymph nodes was observed in advanced stages of lymphedema. Bacilli and cocci were sensitive to gentamicin, tetracyline, rifampicin, vancomycin, kanamycin and cotrimoxazole, and least sensitive to penicillin. Blood cultures of patients in the periods between DLA attacks were negative. In healthy controls without edema and episodes of DLA, tissue fluid did not contain bacteria. In lymph, only single colonies of Micrococcus and Acinetobacter were cultured in 12% of the cases. Impaired lymph drainage and lack of elimination of penetrating bacteria may be responsible for progression of lymphedema and recurrent attacks of DLA.