Infantile asthma is a bronchial asthma seen in infants under two years of age. A few reports have been made of infantile asthma, but many retrospective studies about childhood asthma revealed that 25 to 50% of asthmatic children had had the first episodes of asthma before two years of age. For the purpose of identifying this clinical entity, 43 cases of asthmatic infants experienced in the last five years were studied from the clinical and laboratory viewpoints. 1) Male is dominant in number and strongly positive history of allergy was found in infants as well as in their family members. 2) The asthmatic infants had had frequent cold before they had attacks and the first attack of asthma was experienced by 90% of them after 6 months of age. 3) The leucocytosis and fever were very slight in grades. 4) The levels of eosinophilia in blood smear, nasal secretion, and sputum and positive skin reactions to many kinds of allergens were observed low in the studied compared with the chilhood asthma. 5) Blood gas analyses undertaken during attacks showed abnormal patterns in 71% of the subjects and predominant hypoxia ranged between 54 and 69 mmHg. 6) The virological and bacteriological studies were made both during attacks and convalescences. 7) Histaminopexic activity of the serum by the method of Latex-histamine showed almost the same cumulative distribution table as childhood asthma. Immunoglobulins (IgG, IgM, and IgA in serum) measured in 24 cases were all within normal limits. 8) Diagnostic criteria in our clinic were present.