The intervals between arrival or rearrival in the UK and notification of tuberculosis have been studied in four groups of Asian immigrants according to contact with known cases of tuberculosis in the UK and recent visits to Asia. It appears that about one-fifth of the Asian immigrants who developed tuberculosis in West Ham in a 5-year period did so as a result of a recent visit to Asia. About one-third appeared to have acquired their infection before leaving Asia and developed the disease soon after arrival in the UK. Nearly one-half apparently acquired their disease from known or unknown contacts in the UK.