The cerebrospinal fluid values obtained in the first 12 weeks of life from 43 infants with birth weights of 1500 gm or less were analyzed to determine the ranges for leukocyte count and chemistry values. All these neonates had birth weights appropriate for gestational age, negative cerebrospinal fluid culture for bacteria, and no evidence of intracranial bleeding by head ultrasound examination. The mean birth weight was 1002 gm (range 550 to 1500 gm), and mean gestational age was 27 weeks (range 24 to 33 weeks). The mean cerebrospinal fluid leukocyte count was 5 cells/mm3 (range 0 to 44 cells/mm3); leukocyte differential was 7% polymorphonuclear leukocytes (range up to 66%) and 85% mononuclear leukocytes (range 13% to 100%). Additional values included protein concentration, 142 mg/dl (range 45 to 370 mg/dl); and glucose, 60 mg/dl (range 29 to 217 mg/dl). Knowledge of these measurements should help in the interpretation of the cerebrospinal fluid values of the very low birth weight infant undergoing examination of a central nervous system disorder.