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Flower bud development of apricot cultivars can be studied during dormancy period by different methods (forcing of shoots, measuring of bud weight and water content, observing of pistil elongation, study of micro-sporogenesis). In our 24-year experiment, the phenological process of microsporogenesis of three apricot cultivars ('Cegledi biborkajszi', 'Gonci magyar kajszi' and 'R6zsakajszi C.1406') was studied. We could fmd great differences in the process of microsporogenesis between three cultivars and between years as well. During this long-term period, the string stage (end of endodormancy) occurred gradually later (more than half a day later per year), but tetrad stage and blooming time occurred gradually earlier. As a trend of 24 years, tetrad stage shifted 8-19 days earlier, and the beginning of blooming time is 3 days earlier. The reason for the observed trends is probably due to the regional warming of the climate, which has a strong effect in the Carpathian Basin. Because of regional warming, winters are getting milder at our site as well. In the milder winters, it takes longer time to collect the necessary chilling units, thus the end of endodormancy occurs later. But the heat unit accumulation is faster during ecodormancy, which means that the phenological processes are accelerated and blooming occurs earlier.