The ratios of 214Bi to 214Pb in the surface atmosphere at Bombay on the west coast of India have been measured. In all, about 500 measurements were carried out at the ground surface and on top of a building 20 m high. The analysis techniques consisted in the least squares resolution of the alpha decay curves of high volume air filter samples counted by using large ZnS scintillation detectors. The collection and counting periods were optimized for minimizing the errors. The sample collection procedure consisted in taking a morning and an afternoon sample everyday. The measured ratios varied from 0.3 to 1.0, the average values being in the range 0.6-0.9. The afternoon ratios were generally higher than were the morning values. The data also showed that during late winter and spring the ratios reached the minimum values observed during the year. The possible reasons for the variations in the measured ratios are discussed.