The frost tolerance of 12 peach (Prunus persica (L.) Batsch) varieties was determined in artificial freezing tests, while the developmental rate was examined through microscopic study of microsporogenesis. The frost tolerance of flower buds continuously increased from autumn till December, then started to decrease. There was a high correlation between the rate of microsporogenesis and the change of cold hardiness of the flower buds during winter. The slower the rate of microsporogenesis the better the cold hardiness of a variety. 'Piroska', a native Hungarian variety had slow microsporogenesis and the best frost tolerance. Of the foreign varieties, the frost tolerance of 'Champion' was the best. In addition 'Early Redhaven', 'Harko', 'Redhaven' and 'Babygold 6' possessed a suitable level of frost tolerance. The floral bud developmental rate was quick for the varieties 'Fairlane', 'Red June' and 'Michelini', which was paralleled by quick decrease of their frost tolerance in the second half of winter. 'Venus', 'Springcrest' and 'Mayfire' are not recommended for Hungary, due to their poor frost tolerance.