Young dogs were divided into the following 3 groups. Group 1: Reared with normal food in a normal temperature for 30 days (4 dogs). Group 2: Reared on a low protein diet in a normal temperature for 30 days (5 dogs). Group 3: Reared on a low protein diet in high temperature and high humidity for 30 days (5 dogs). Serum protein fractions of each of these 3 groups were electrophoretically studied and compared each other. The results were as follows: In group 1. total protein, albumin and γ-globulin content increased 117%, 117% and 142%, respectively, during this period as compared with those before this experiment. In group 2, total protein and albumin content decreased to 74% and 28%, respectively, as compared with those before this experment, but γ-globulin content increased to 145%. In group 3, total protein and albumin content remarkably decreased to 63% and 20%, respectively, but γ-globulin content increased to 114%. However this increase is smaller than in other groups. These results indicate that when low protein diet is given, arbumin decreases but γ-globulin does not decrease, and only after the mesenchymal function is damaged by high temprature and high humidity does hypo-γ-globulinaemia occur. From this fact it is thought that hypo-γ-globulinaemia in patient with Jusho-shokafuryosho is due to mesenchymal functional disturbances caused by high temperature and high humidity rather than due to low protein feeding that the human infant in the weaning period is apt to receive.