A study of the effects of agents on reproduction of the American alligator requires precise definitions or relevant parameters. A definition should specify the unit described (lake, pen, animal or group of animals considered) and allow assignment of numerical values. For example, nest rate may be calculated for the population, lake, pen, adult female(s), all breeders (male and female) or the entire colony but it usually means the percentage of adult females which make a nest. By definition an egg must have yolk, white and a membrane. The average alligator egg has a volume of 65 (+/- 10) cc, deviates less than 5% from being spheroid in shape and has a major/minor axis ratio of 1.7 (+/- 0.02). Normal egg composition is 43.9 (+/- 2.1) % yolk, 43.5 (+/- 2.1) % white 10.5 (+/- 0.7) % shell and 1.75 (+/- 0.3) % membrane. Clutch size is 45 (+/- 4) for the major lakes in Florida. Fertile eggs are those which show grossly visible membrane attachment or permit bacterial growth within 2 weeks of collection. Normal egg fertility should be greater than 80 %. The conceptus is an embryo until lung development permits pulmonary respiration and then it is considered a hatchling. Reproductive rate is defined by the number viable hatchlings produced per unit each year. A viable hatchling is one with sufficient vigor to reach commercial size during a defined grow out period. Vigor is equal to performance (Average of growth rate plus body condition) for an individual or performance minus death rate for a group. The use of defined parameters permits a designation of infertility (production of less than 12 viable hatchlings per adult female) and a study of factors or agents which affect fertility.