The distribution of calving hours in the dairy cow was described and analyzed through a 2 550 sample relative to 3 breeds: Holstein, French-Friesian, Montbeliarde (table I). Calving data (n = 2 031) from suckling cows were used for comparison. All the data concerned cows kept in stanchion stables during the winter period (October to March) in 2 experimental farms in the mountain area of central France. The observed distributions for dairy cows differed from that of suckling cows, which was more homogeneous; differences were observed between farms, but not between dairy breeds within farms (fig 1 and table I). The rhythm of the presence and activity of cowmen explains the major pattern of calving hours (tables III and IV). In the dairy cow, the mean diurnal frequency of occurrence of calving was higher when cowmen were absent (46.4/1 000) than when they were present (35.3/1 000); the lowest frequency occurred during milking (28.9). Difficult parturitions occurred more frequently at daytime human interventions being scarce at night (fig 2). Consequently, diseases linked to calving concerned more daytime parturitions. We could not prove any effect of the lactation rank, the milk yield in the first week, or calf sex or birth weight