Recent anecdotal reports have touted the gastrointestinal (GI) hormone secretin as a treatment modality for autism, though there is little clinical evidence or literature to support its viability. We undertook a two-part clinical trial to investigate these claims. Fifty-six patients (49 boys, 7 girls, mean age = 6.4 years, SD = 2.7) enrolled in an open-label trial of secretin, during which they received one injection of the hormone (2 IU/kg). All subjects were evaluated by their parents at baseline and follow-up visits (3-6 weeks later, M = 3.7, SD = 1.4 weeks) with Childhood Autism Rating Scales (CARS). Thirty-four patients were labeled with Pervasive Developmental Disorder Not Otherwise Specified, and 22 met diagnostic criteria for Autistic Disorder. Forty-five patients were concurrently on other drug treatments. At follow-up, some reported minimal but potentially significant improvements including changes in GI symptoms, expressive and/or receptive language function, and improved awareness and social interactions. No adverse effects were reported or observed. Subsequently, 17 of the most responsive patients from Study 1 began a double-blind trial that also included 8 newly enrolled patients. Patients in this second study were alternatively entered into one of two groups and received injections of secretin or placebo with crossover at 4 weeks. Patients from Study 1 entered into Study 2 at an average of 6.5 (SD = 0.8) weeks after beginning Study 1. Results of both inquiries indicate that although treatment with secretin was reported to cause transient changes in speech and behavior in some children, overall it produced few clinically meaningful changes when compared to children given placebo injections.