A radiation-induced adaptive response has been convincingly demonstrated in a variety of cultured cells. It is associated with the activation of genes and the up-regulation of protein enzymes, resulting in a delay in cell-cycling and the opportunity to repair radiation-damaged DNA as a transient phenomenon. Just how the adaptive response operates in a multi-cellular organism is still obscure, but there is little or no evidence in rodents and the beagle dog of a shortening of lifespan after exposure to acute doses up to a few hundreds of mGy or after chronic daily exposure resulting in accumulated doses of up to a few Gy. Nevertheless there is an increase in both non-neoplastic and neoplastic diseases which need not be life-threatening. A prudent approach has been used by the 1CRP in deriving a value for radiation-induced detriment at low doses from which to recommend individual dose and risk limits in their system of radiological protection. This is not to deny the possible existence of an adaptive respo A radiation-induced adaptive response has been convincingly demonstrated in a variety of cultured cells. It is associated with the activation of genes and the up-regulation of protein enzymes, resulting in a delay in cell-cycling and the opportunity to repair radiation-damaged DNA as a transient phenomenon. Just how the adaptive response operates in a multi-cellular organism is still obscure, but there is little or no evidence in rodents and the beagle dog of a shortening of lifespan after exposure to acute doses up to a few hundreds Of there is an accumulated in of doses of up to a few Gy. Trends there is an increase in both non-neoplastic and neoplastic diseases which need not be life-threatening. A prudent approach has been used by the 1CRP in deriving a value for radiation-induced detriment at low doses from which to recommend individual dose and risk limits in their system of radiological protection. This is not to deny the possible existence o f an adaptive respo