Abstract. -ethyl] carbamate) is an insect growth regulator used for long-term fire ant control. Because of its effects on insect reproduction and its potential use on pasturage consumed by food animals, a reproductive study was conducted using Rambouillet sheep. The sheep were dosed daily with a placebo or with fenoxycarb at 0.69 or 1.38 mg/kg/day, representing ten (10ϫ) and 20 times (20ϫ) the maximum amounts of fenoxycarb in forage or hay treated at recommended levels for fire ant control. Parameters that were measured included rates of weight gain of adults, serum clinical chemistry profiles of adults, spermatozoal morphology and motility, estrus cycling, pregnancy rates, maintenance of pregnancies to term, numbers of live births, and rates of weight gain of lambs to 28 days. There were no statistically significant (P Յ 0.05) differences between the exposed and control groups of sheep in any of these facets of the study. No clinical signs associated with exposure to fenoxycarb were observed in any animal at any time, and no exposure-related pattern of pathologic lesions or reproductive organ histology was observed. Means of hepatic fenoxycarb residues in the rams followed a statistically significant (P Յ 0.05) dose-related pattern. No fenoxycarb was detected (detection limit of 5 ppb) in any neonatal liver, despite the presence of hepatic fenoxycarb residues in the treated ewes, indicating that transplacental transport of fenoxycarb was minimal. No fenoxycarb was detected in any lamb liver at 28 days, although both the colostrum and the milk of exposed ewes were found to contain fenoxycarb at levels proportional to the treatments. Based on the lack of significant findings in this study, it is unlikely that use of fenoxycarb, according to label instructions (currently applicable to homeowner and registered agricultural usage) for fire ant control in pasturage or hay fields, will affect ruminant reproduction.Fenoxycarb (ethyl [2-(4-phenoxyphenoxy)-ethyl] carbamate), a despite its structure, does not act as a carbamate cholinesterase inhibitor. 15 As an insect growth regulator, it strongly stimulates juvenile hormone activity, thus inhibiting molting and metamorphosis between growth stages (larvae, pupae, and adult) and also suppressing egg development. 9,20,21 Fenoxycarb is available in several sectors of the pest control market with demonstrated efficacy in the control of fire ants, 9-11 mosquitoes when it is applied to standing water, 21,22 and cockroaches 16 and fleas 20 in laboratory situations. In the form of a granular bait on a defatted corn-cob grit base, 23 fenoxycarb is used by commercial pest control operators and homeowners to suppress the infiltration of fire ants (red imported fire ants, Solenopsis invicta) in urban and registered agricultural sites. Fenoxycarb thus far is not labeled for food animal pasture use, although the impact of fire ants has been noted by both cattle raisers 3 and wildlife management personnel. 3,5 The ants swarm onto any animal that is on Received for publication December ...