In a prior pilot study involving six children, we noted improved memory and concentration and improved behavior when these children were switched from theophylline to cromolyn sodium therapy. We now report the findings in 29 children (24 boys and five girls), aged 7 to 12 years. In this study, a double-blind, double-dummy randomized design was used so that half the subjects continued to receive theophylline and the other half was actually switched from theophylline to cromolyn sodium therapy. Assessment again consisted of the revised Wechsler Intelligence Scale for Children, the Selective Reminding test, the Benton Visual Retention test, Stroop tests I and II, and the Child Behavior Checklist. The group receiving placebo theophylline/active cromolyn sodium therapy demonstrated greater improvement on all tests of memory and concentration, with greatest significance for the Stroop test (p less than 0.03 by analysis of covariance). There were also significant correlations between length of time theophylline was taken and scores on the depression (p less than 0.03) and the obsessive-compulsive (p less than 0.04) subscales of the Child Behavior Checklist. These results support the findings of the previous pilot study but, in addition, raise concern about depression and anxiety as possible long-term side effects of long-term theophylline therapy.