Profiles of free amino acids in cerebrospinal fluid (CSF) were determined by high-performance liquid chromatography for 20 nonneurologic control patients and 12 patients with infantile spasms. Statistical comparisons showed significantly elevated levels of lysine (p less than 0.001) and the excitatory neurotransmitter, glutamate, (p less than 0.01) for the infantile spasms group as compared to the nonneurologic control group. When the infantile spasms patients were subdivided according to the presence or absence of etiologic associations, highly elevated amino acid levels were observed only in CSF from patients of the symptomatic subgroup. The idiopathic subgroup showed levels of free amino acids that were not statistically different from those of the nonneurologic control group. These results indicate that while abnormalities of amino acid metabolism often accompany infantile spasms, no specific pattern of the major free amino acids in CSF appears to be directly related to this seizure disorder. Elevated levels of the excitatory amino acids, aspartate and glutamate, do not necessarily accompany infantile spasms, and in this study were only observed in symptomatic patients.