A survey of 393 Puerto Rican and 354 non-Hispanic pediatric patients at Beth Israel Hospital, New York, revealed a significantly larger percentage of asthmatic subjects among Puerto Ricans, confirming findings of a study of Puerto Rican adults in New York. Assays of alpha 1-antitrypsin (AAT) concentration and phenotypes in 61 Puerto Rican asthmatic children revealed a significantly larger number with an S or Z variant in AAT phenotype. The AAT concentration was not a significant variable in this relationship, since four of five subjects with intermediate deficient AAT concentrations and a PiM phenotype were among control nonasthmatic Puerto Rican subjects. A family history of asthma was more common among asthmatic than control subjects and was most common for variant AAT phenotypes in either asthmatic or control subjects. We speculate that the S or Z variant of AAT affects the inflammatory response in such a way as to predispose to asthma.