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Abstract Skeletal variations were studied in 20‐day rat fetuses from pregnant females given acetazolamide, actinomycin D, or sodium salicylate and in vehicle‐treated and untreated controls. A slight increase over untreated control values as regards resorptions, malformations, and certain skeletal variants was noted in some vehicle‐treated groups. Supernumerary 14th ribs were designated as rudimentary (less than half the length of the 13th rib) or extra (half or greater than half the length of the 13th rib) on the basis of actual measurement showing a bimodal distribution in length. The occurrence of rudimentary 14th ribs was highly variable after vehicle or teratogen treatment. Extra 14th ribs occurred in a dose‐related fashion after actinomycin D (days 7 and 9) and sodium salicylate (which sometimes also produced 15th ribs), but not after acetazolamide treatment. Sternebrae were variable in form after most treatments and these changes showed a slight but insignificant increase after actinomycin D or sodium salicylate on day 9. The incidence of variations of vertebral centra was highly changeable after all treatments but was consistently greater after sc treatment with water or acetazolamide and appeared to be dose related after sodium salicylate. The authors believe that none of these skeletal variants should in themselves be considered as malformations. The possibility exists that extra 14th ribs could be regarded as indicators of teratogenic potency of a drug at some higher dosage; but the data presented did not demonstrate the usefulness of the other skeletal variants examined as signals of teratogenic potential.