AbstractAbnormal development of the embryonic axis is one consequence of injection into the yolk sacs of 48‐hour chick embryos of each of the following teratogens: actinomycin D, puromycin, deoxyguanosine. Rumplessness and trunklessness are consequences of treatment with actinomycin D or puromycin; thoracic constrictions are consequences of treatment with deoxyguanosine. Treatment with both actinomycin D and deoxyguanosine, under certain conditions of dosage and developmental timing, results in an increase in the frequency of rumplessness and trunklessness; the same is true for combined treatment with puromycin and deoxyguanosine. Although deoxyguanosine treatment of 72‐hour embryos is also associated with rumplessness, evidence is presented that deoxyguanosine‐induced rumplessness does not contribute to the effects obtained with embryos treated at 48 hours incubation age with these combinations of teratogens. Treatment with both actinomycin D and deoxyguanosine can result in an increase in the frequency of thoracic constrictions; treatment with both puromycin and deoxyguanosine, in a decrease. These interactions in teratogenesis between deoxyguanosine and actinomycin D and between deoxyguanosine and puromycin indicate that the distribution in the embryo of each teratogen is more widespread than suggested by the morphological consequences associated with each individ