The objectives of the current trial were to characterize the changes in the ultrasound image of preovulatory follicles at ovulation in does and to determine the usefulness of ultrasonography in studies involving the evaluation of time of ovulation. The study involved 12 goats in which oestrus was synchronized with three prostaglandin F2α, cloprostenol injections. Ultrasonographies were performed every 4h from 48h after the third cloprostenol administration. The presence of at least one preovulatory follicle (mean diameter of 7.8±0.4mm) was found in all the does at the time of the first scan. In comparison to other large diameter non-ovulatory follicles, preovulatory follicles had irregular outlines and diffuse and heterogeneous hypoechogenicity in the antrum, with reverberation artefacts similar to echoic spots and echoic lines in some cases. Occurrence of follicular evacuation and ovulation may be determined by the disappearance of the follicular antrum. The corpus haemorrhagicum was found to consist of a heterogeneous structure (mean diameter of 8.6±0.3mm) with higher echogenicity compared to the preovulatory follicles. On the basis of disappearance of the preovulatory follicle and visualization of increased heterogeneous echogenicity in its site, serial ultrasonographic evaluation was found to be useful in establishing the time of ovulation in goats. However, the similarity in the echoic pattern of the corpus hemorraghicum and the surrounding ovary may complicate the identification of ovulations in isolated observations. © 2003 Elsevier B.V. All rights reserved.