A method for regulating the growth processes in a myriad of cells, tissues, organ systems and unicellular and multicellular organisms including plants, animals and man by the administration of effective amounts of the opioid antagonists naloxone, naltrexone, their analogs, metabolites derivatives, and/or mixtures thereof. At the cellular level, the growth processes entail all mitotic events and related processes including cell proliferation, as well as cell migration and cell differentiation, and at the somatic or organismal level, anatomical, behavioral and neurological development, metamorphisis and maturation. Growth regulation can be effected in vivo and/or in vitro.