A method is described for the quantitative determination of phenobarbital in blood plasma by means of fused silica capillary columns and splitless sample introduction. Several factors that influence the splitless sample introduction are evaluated. Using a simple column isolation procedure without derivatization prior to GC analysis, recoveries over 80% were found with a precision corresponding with a standard deviation of about 5%. Concentrations ranged from 5-25 mg/l. With a flame ionization detector a detection limit of 0.5 mg/l was observed so that the procedure can also be useful for barbiturates with lower therapeutic plasma levels.