We studied the effects of β-casomorphins (β-CMs, μ-acting opioid peptides from milk protein β-casein) on survival of primary-cultured chick dorsal root ganglion neurons in the presence of nerve growth factor. β-CM-5 and β-CM-7 had potent neuronal survival-promoting activities. β-CM-4 amide (morphiceptin) and des-Tyr¹-β-CM-7 also exhibited the similar promoting effects, although their effects were very weak. The promoting effect of β-CM-5 was prevented by co-administration of naloxone, or pretreatment with pertussis toxin. These results suggest that the neuronal survival-promoting effects of β-CMs might be mediated through opioid receptors coupled to G proteins.