The results of first and second inseminations carried out by the associations of artificial insemination of Sijbekarspel and Stompetoren during the period from November 1971 to November 1972, were studied more closely. The reason for this study consisted in the fact that there were systematic differences in the results of 60-90 days non-return after first inseminations between the two associations. Although the size of the farms (determined by the number of first inseminations) actually had an effect on the results of the inseminations within the herds of the two associations, this cannot account for the difference between the two associations. The effect of the size of the farms, summarized in the concept of management, is also determined by the choice of bulls. The milk-production level did not have any overall direct effect on the results of insemination.