Water hyacinth is the most serious aquatic weed in India, infesting more than 200000 ha of water surface. Successful biological control of this weed was achieved in a fully infested tank covering 20 ha at Bangalore. More than 95% of the infestation was cleared within 32 months by releases ofNeochetina eichhorniaeWarner. The insect also spread along a water channel and controlled water hyacinth infesting a nearby tank. Drying up of the tank after the insect population had spread throughout and increased to 3.1 adults/plant hastened weed control. Fresh plants emerging after rains were suppressed by the residual population of insects.N. eichhorniaealong withN. bruchiHustache is being supplied to centres throughout the country for multiplication and releases. Sustained efforts with these insects holds out promise of control of water hyacinth in India.