AbstractPyridine‐2‐aldoxime methiodide and pyridine‐2‐aldoxime methyl methane sulfonate (P2S), used as supplements to carbachol or neostigmine, greatly lowered the incidence in chicken embryos of vertebral defects and muscular hypoplasia. With 4‐pyridine aldoxime the effect of the teratogens was less reduced. Supplementation of carbachol or neostigmine with either ambenonium or toxogonin lessened the occurrence of muscular hypoplasia, but did little, if anything, to prevent malformation of the neck vertebrae. In tests with physostigmine P2S as supplement reduced or prevented cervical defects, but failed to protect the nicotinamide‐sensitive parts of