PIP: Previous studies have observed a 7-day cycle with the least number of births occurring on Sundays. This study was aimed at characterizing the daily effect on the number of births in Israel, where Sunday is a regular working day and Saturday is a nonworking day. It was hypothesized that fewer births would be noted on Saturday rather than Sunday and fewer births on Jewish holidays. The data consisted of a random sample of live births during 1975. A robust time series procedure was used for the data analysis. As expected, the number of births was much smaller on Saturdays than on other weekdays (10% reduction). The seasonal component for Sundays was greater than that for any other day due to births delayed from Saturday and scheduled induced births. The number of births was not reduced as much on Saturdays during spring and summer as during fall and winter. In addition, fewer births occurred on most Jewish holidays. However, an unexpected and extremely high number of births was noted on Yom Kippur and the day after. It is speculated that the strain and fasting during this holiday promoted labor induction. In 21 of the 52 weeks in the study period, the least number of births occurred on a Saturday, and the number of births was less than the mean of the remaining 6 days in 46 of these weeks. Similarly, in 17 of the 52 weeks, the greatest number of births occurred on a Sunday, and the Sunday births exceeded the mean of Monday-Friday births in 35 of these weeks. Thus, these results confirm the study hypothesis and are believed to reflect intervention in childbirth.