[Possible effect of natural background radiation on the development of mammals].

The deceleration of the development of young rats during the postnatal ontogenesis under conditions of a low-background chamber (a 10-fold decrease in the natural radiation background) was detected using the criterion of individual growth of the body weight for 10 days of observation. The administration, to the low-background chamber, of uranium salts which restore the natural background (all other experimental conditions being retained) removed the effect observed.