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Status, breeding, and foraging of Chatham Island tui (Prosthemadera novaeseelandiae chathamensis) were studied on Rangatira Island, Chatham Islands between January 1995 and May 1999, with short visits made to adjacent Pitt Island throughout this period. The total population was estimated at ≈260 adults. Most birds were resident on Rangatira Island in spring, summer and autumn but moved to Pitt Island during the winter. In spring birds commuted between the two islands but became resident on Rangatira when breeding commenced. Radio transmitters were attached to adult tui to monitor breeding. No radio-tagged females bred (n = 13) but at least two of three radio-tagged males raised young. Adult tui were intolerant of disturbance during nesting so estimation of productivity was made by mapping the number of fledgling groups. Flax (Phormium tenax) nectar appeared to be the most important food for breeding tui and birds travelled long distances to visit flowering plants. Fruits of ngaio (Myoporum laetum), matipo (Myrsine chathamica), karamu (Coprosma chathamica), mahoe (Melicytus chathamicus) and muehlenbeckia (Muehlenbeckia australis) were also important foods. Invertebrates were most important when females were feeding their young. The amount of breeding that occurred each season was directly related to the abundance of flax flowers in spring, and in good flax flowering years tui were able to rear two broods. In poor flax flowering years many birds did not breed. Control of feral cats on Pitt Island would most likely result in a significant increase in this breeding population; however planting of flax adjacent to the forest areas on Chatham Island along with predator control may be necessary before tui can re-establish there.