CURRENT literature contains confusing reports about the number and nature of the free amino-acids normally present in human cerebrospinal fluid1. Thus, while some investigators have detected only three to eight amino-acids2, others have found as many as eighteen3. In many instances, a particular amino-acid was not present regularly, but was only observed in a few cases. For this reason, reports which suggest that certain amino-acids occur exclusively in certain diseases can only be regarded as speculative. The aim of the present work has been to establish whether or not a regular pattern of amino-acids exists in normal and abnormal cerebrospinal fluid.