Normal vertebrate development requires appropriate amounts of Vitamin A and retinoic acid (RA), yet exogenously supplied Vitamin A metabolites cause teratogenic effects. All-trans retinoic acid (all-trans RA) and 9-cis retinoic acid (9-cis RA) are potent metabolites of Vitamin A and operate by binding to retinoic acid receptors that are transcription factors. These isomers directly affect gene expression by the binding of all-trans RA or 9-cis RA to retinoic acid receptors (RARs) and the binding of 9-cis RA to retinoid X receptors (RXRs). In zebrafish, exogenous application of the retinoid isomers is known to have deleterious effects of varying magnitudes on development; however, little is known about the comparative effects of 9-cis and all-trans RA on the development of Japanese killifish (Oryzias latipes) embryos. In this study, we report the effects of exposing neurula embryos to concentrations of retinoids ranging from one micromolar to one nanomolar for 72 hours. The data indicate a dose-dependent inhibition of hatching irrespective of the retinoid isomer used. In addition, heart formation and cranial structure development are inhibited in a dose-dependent manner with both all-trans and 9-cis RA. Concentrations of 9-cis and all-trans RA below .01μM result in hatching of apparently normal fry.