Isoenzymes of aldehyde dehydrogenase in human lymphocytes. The types of isozymes of aldehyde dehydrogenase (ALDH) present in human lymphocytes has been investigated using isoelectric focusing of polyacrylamide gels followed by substrate-specific staining. Lymphocytes obtained from most individuals were found to contain both types I and II ALDH. This group of 'typical' individuals reported that they did not develop marked facial flushing or rapid heart rate after drinking alcohol nor did they develop an erythema to cutaneously applied ethanol. Lymphocytes obtained from 'atypical' individuals who do suffer from alcohol-induced flushing and rapid heart rate and who developed erythema to cutaneous ethanol displayed type II, but not type I, ALDH. Lymphocytes thus appear to be an easily accessible and suitable tissue for determining type I ALDH phenotype. 