PSK was administered to the retired workers of the Poison Gas factory who showed high incidence of malignancy and immunological abnormalities. Furthermore, changes of various immunological parameters were studied. In the group in which Leu 1 positive rate showed a low value, Leu 1 positive rate showed significant increase after PSK administration. NK cell activity as well as Leu 7 positive rate showed significant elevation after PSK administration. It seems that PSK potentiates the immunity of non-tumor bearing individuals with depressed immunity.