The effect of a novel polyherbal formulation BASANT on Chlamydia trachomatis was studied. In vitro sensitivity testing was done by direct exposure of C. trachomatis (pre-infection incubation with BASANT) and exposure of C. trachomatis within HeLa 229 cells (post-infection incubation with BASANT). Pre-infection incubation of standard serovar D/UW-3/Cx with BASANT showed complete inhibition after 60, 30 and 15 min of incubation at concentrations of 12, 30 and 60 microg/mL, respectively. In the post-infection incubation, 8-10 microg/mL of BASANT showed complete inhibition of standard serovar D/UW-3/Cx as well as of five clinical isolates of C. trachomatis after 48 h of incubation. BASANT also inhibited a clinical isolate obtained from a doxycycline treatment failure patient at a concentration of 30 microg/mL. Both assays with standard and clinical isolates showed that BASANT has antimicrobial activity against C. trachomatis, suggesting the potential clinical utility of BASANT for the prevention of C. trachomatis infection by the sexual route.