Background: 14-3-3 proteins are major evolutionarily conserved cytosolic proteins that regulate signal transduction, apoptosis and neurotransmitter synthesis. Five homologous 14-3-3 isoforms, beta, gamma, zeta, epsilon and eta, are reported in mammalian neurones. To elucidate the diagnostic value of 14-3-3 in cerebrospinal fluid (CSF), a highly specific antibody against each isoform and studies on the isoform patterns in patients with neuronal destruction are needed, Methods: In this study, we raised isoform-specific antibodies against 14-3-3 proteins and established a semiquantitative method of identification of each isoform by Western immunoblotting. Results: We found that three isoforms, 14-3-3 epsilon, gamma and zeta, appeared in the CSF of HIV patients with AIDS dementia complex or cytomegalovirus encephalitis, but not in AIDS patients without neurological symptoms or the non-HIV patients examined. The isoform patterns in AIDS patients were different from those reported in Creutzfeldt-Jakob disease and herpes simplex encephalitis, suggesting that the isoform patterns may facilitate the differential diagnosis. A high frequency of 14-3-3 in CSF was observed in seriously ill AIDS patients, particularly those with CD4 levels of less than 20 mm(3). Conclusion: These findings suggested that 14-3-3 proteins were released from destroyed neural cells and are useful real-time markers of the rate and amount of neural cell destruction in these patients. (C) 2001 Elsevier Science B.V. All rights reserved.