1. Other labs have reported using a continual "minipump" delivery of porcine FSH (11) to rats instead of IP injection of the hormone to yield 60-100 eggs/ rat, but Waller et al. (8) found that only a small percentage of treated rats ovu-late and mate.

2. In the light-dark cycle described, males will copulate with females at around 0030 h. Fertilization occurs 30 min to 2 h later. Harvesting the eggs between 1000 and 1130 h of the same day gives a subsequent window of 12 h during which the eggs can be injected. After this time, the fertilized eggs will start to undergo the first cleavage division to give two-cell embryos—injections near this time-point may result in chimeric animals.

3. Pseudopregnant females 0.5 d pc can be implanted with microinjected eggs anytime during the day following an infertile mating.

4. For superovulating mice, we routinely inject at 1030 h for both FSH and hCG.

5. Occasionally, a high proportion of eggs from superovulated rats are unhealthy or unfertilized. In this instance, consider switching FSH and hCG injection times to 1100 and 1200 h, respectively.

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