Three groups of age- and PIQ-matched children (Autism, Receptive Developmental Language Disorder, and normal controls) participated in two event-related brain potential (ERP) experiments. Each of these experiments was aimed at evaluating whether either of the two clinical groups of children demonstrated abnormalities in two auditory ERP components, N1 and P2, which are known to be dependent on stimulus characteristics (frequency, intensity, and probability), and believed to be generated within primary and secondary cortex. Results of Experiment 1 provide partial support for the idea that both clinical groups failed to fully process changes in stimulus intensity as indexed by the N1 component. Results are discussed in reference to potential abnormalities in serotonergic regulation of auditory cortex.