In this study we investigated the temporal relationship between ovulation, egg formation, oviposition and the changes in plasma concentrations of progesterone, luteinizing hormone and estradiol-17 beta during the egg laying cycle in farmed ostriches. In 10 egg-producing birds, transcutancous ultrasound scanning was performed at 3 h intervals and blood sampling at hourly intervals during a period of at least 48 h (one egg laying cycle). In hens (n = 8) that ovulated during the observational period, the ovulated egg was first detected 2 It after oviposition; thus, ovulation occurred shortly after oviposition in all birds. During the period between two consecutive ovipositions, the developing egg remained for 9 It in the proximal part (infundibulum, magnum or isthmus) and for 39 It in the distal part of the oviduct (uterus). In ovulating hens, plasma progesterone concentrations showed a characteristic and consistent profile: from basal levels of around 0.1 ng/ml concentrations started to increase 12 It before oviposition, reached an average maximum of 3.5 ng/ml at 3 h before oviposition and returned to basal levels 3 h and 30 min after oviposition. Changes in plasma luteinizing hormone and estradiol-17 beta concentrations showed comparable patterns of elevation and decline relative to the timing of oviposition and ovulation. However, variation in their individual basal concentrations was generally larger and peak values were less conspicuous than those of progesterone. In non-ovulating hens (n = 2) neither progesterone, nor luteinizing hormone nor estradiol-17 beta showed elevations to peak concentrations before oviposition. These data demonstrate that during the egg laying cycle of ostriches, events such as ovulation, egg development and oviposition evolve according to a rather strict time schedule, and that progesterone, luteinizing hormone and estradiol-17 beta reach peak concentrations shortly before ovulation. Additionally, our findings also show that on-farm ultrasound scanning is a useful technique to discriminate between ovulating and non-ovulating hens. (c) 2006 Elsevier Inc. All rights reserved.