A simultaneous GC analysis of more than 20 amino and nearly 30 non-amino organic acids abundant in plasma is for the first time possible. Isolation of the analytes from the plasma matrix is not necessary, keto acids do not require a preliminary oximation. An instantaneous derivatization of the acids with ethyl chloroformate takes place directly in the medium after deproteinization. Less than 30 min are required to prepare a plasma sample for the GC analysis.