Cats were initially exposed to 50 Brugia malayi larvae on one hind foot. Later they were re-exposed on the same foot to an additional 50 larvae; the contralateral leg was never exposed to filariae. From 3 to 6 months after reinfection they were challenged on both hind legs with a Group G beta hemolytic streptococcus originally isolated from a spontaneous lesion concomitant with a Brugia infection. There was essentially no observable change in limbs not previously exposed to Brugia. In contrast, 9 of 10 Brugia-infected legs showed evidence of lymphangitis and bacterial proliferation causing necrosis, draining abscesses, cellulitis, edema or erythema. This study demonstrates that repeated infections with B. malayi may result in a significant increase in susceptibility of cats to streptococci. Use of this model should enable additional studies to clarify the role of secondary microbial infections in disease generally ascribed to filarial infection.