The results of this study indicate that there was no ben-eficial effect of addition of 5 mg of prostaglandin F2 at the time of insemination nor any interaction with the number of frozen-thawed sperm used on final pregnancy rate or lit-ter size. This was unexpected since prostaglandin added tosemen in a low fertility model using 0.5 billion sperm witha single insemination increased numbers of fetuses andnumerically increased sperm in the reservoir