Recent evidence in the cow suggests that endothelin-1 (ET-1) plays a role during prostaglandin (PG) F_2α-induced luteal regression. We have examined the effects of treatment with PGF_2α during the early and midluteal phases on three components of the endothelin system: endothelin-converting enzyme-1 (ECE-1), ET type A receptor (ET_A), and ET-1 in the bovine corpus luteum (CL). Cyclic beef cows were injected (0 h) on Day 4 or 10 with either saline or the PGF_2α analogue Lutalyse (15 mg). The CL were collected at 2 (n = 11), 10 (n = 23), 24 (n = 15), or 48 h (n = 12) after treatment. The cows in which CL were removed after 10 h comprised of two experimental groups. The first group (n = 11) received one injection; the second group (n = 12) received two injections, one at 0 h and one at 8 h. The cows in which CL were collected after 24 and 48 h received one injection every 8 h. Semiquantitative reverse transcriptase-polymerase chain reaction was used to evaluate the mRNA encoding ECE-1, ET_A, and ET-1. The ECE-1 and ET_A proteins were evaluated by semiquantitative Western blot analysis. The ET-1 was the most likely component of the endothelin system target for PGF_2α regulation during the midluteal phase. The ET_A and ECE-1 genes were constitutively expressed in the Day 4 and Day 10 CL. A practical application of this observation is that it may be possible to target the ET-1 gene as a way to manipulate the luteolytic action of PGF_2α.