Abstract: About 4 strains of kalmegh (Andrographis paniculata Nees.), CIMAP/AP-3, CIMAP/AP-10 and CIMAP/AH-89 and local check were evaluated at three population densities (74,074, 111,111 and 222,222 plants ha-1) for growth behavior, biomass and diterpenoid lactones production at the Central Institute of Medicinal and Aromatic Plants, Lucknow, India during July to November, 2004 and 2005. The strain CIMAP/AP-3 was found to possess desired agronomic traits viz., 60 cm plant height, 45 cm plant spread, 28 branches per plant and 60° branching angle from main shoot. The advantage in biomass and diterpenoid lactones (andrographolide and neo-andrographolide) production with CIMAP/AP-3 over other strains was 33.4-79.4 and 31.6-70.7%, respectively. Planting at a closer spacing of 30x15 cm accommodating 2,22,222 plants ha-1 produced maximum dry biomass and andrographolide and neoandrographolide yield under the subtropical climate of North India.