In a placebo controlled trial, the effects of 21- and 10-day doxycycline treatments (200 mg/day) followed by single dose diethylcarbamazine (administered 4 months post treatment) on depletion of Wolbachia endobacteria from Wuchereria bancrofti, filaricidal activity, and amerlioration of scrotal lymph vessel dilation were studied in 57 men from Orissa, India. The 21-day doxycycline course reduced Wolbachia in W. bancrofti by 94% before diethylcarbamazine administration. After 12 months, all patients with this treatment were amicrofilaremic and different from the 10-day doxycycline (42.9%) and placebo (37.5%) groups, and significantly fewer were positive for scrotal worm nests (6.7%) compared with 10-day doxycycline (60%) and placebo (66.7%). Average scrotal lymph vessel diameters were reduced from 0.7 cm pre-treatment to 0.02 cm in patients after 21 days of treatment, while no significant changes were seen in the other groups. This latter feature confirms the beneficial effects of doxycycline on lymphatic dilation and thus adds to the existing evidence that doxycycline, in addition to being macrofilaricidal, may be used to prevent or reverse lymphatic pathology.