Infantile spasms are an age-related epileptic syndrome of infancy and are characterized by the combination of clusters of epileptic spasms and specific electroencephalographic findings. The etiology and the pathogenesis of the disease is still unclear. Prolactin has been thought to be specifically related to epileptic seizures. To investigate the possible mechanism of prolactin secretion in infantile spasms cerebrospinal fluid prolactin levels were examined. Fifteen patients with infantile spasms (10 females and five males), 3-16 months of age, were evaluated and compared with age- and sex-matched control subject. Cerebrospinal fluid samples for prolactin were obtained before and after treatment. The mean prolactin levels in the cerebrospinal fluid of the patients before therapy (3.25 +/- 1.48 ng/mL) was higher than the control group (2.38 +/- 0.89 ng/mL), and the difference between the two groups was statistically significant (P < 0.001). The mean prolactin level in the cerebrospinal fluid of the patients after therapy (4.69 +/- 1.47 ng/mL) was demonstrated to be higher than the mean prolactin level before therapy (3.25 +/- 1.48 ng/mL) and the difference between the two groups was statistically significant (P = 0.037). Elevation of cerebrospinal fluid prolactin levels before and after treatment in patients with infantile spasms provided evidence that the cerebrospinal fluid prolactin level is related with neuronal injury.