SummaryThe flight activity of two coloniesM. m. marginataand six colonies ofM. m. obscuriorwas studied in São Paulo, Brazil during three periods in 1981–1983. All colonies were hived except for one colony ofM. m. obscuriorwhich nested in a hollow tree. The two subspecies showed the same responses to the climatic factors analysed. Flight activity was correlated positively with temperature and negatively with RH. In favourable conditions foraging took place throughout the day but both species were most active between 11 and 13 h. In the last observation period (October 1982-January 1983), when only twoobscuriorcolonies were studied, flight activity was not correlated to RH, occurring even when RH was unfavourably high. This was a very rainy season, and it is suggested that the behaviour of the bees indicates a flexible response to prevailing weather conditions.