Relations and quocientes of cerebrospinal fluid (CSF) immunoglobulins G (IGG) and serum (S) IGG were studied in 50 patients with chronic headache, normal neurological examination and normal electroencephalogram. CSF was normal as to: pressure, cytology, total proteins, protein fractions and immunoglobulins (IGG, IGA and IGM) contents. In all cases the CSF sample studied was collected from cisterna magna. The relations and quocients studied were: CSF IGG/CSF TOTAL PROTEIN, CSF IGG/CSF ALBUMIN, CSF IGG/CSF PRE ALBUMIN+ALBU-MIN, (CSF IGG/S IGG) / (CSF ALBUMIN/S ALBUMIN) and (CSF IGG/S IGG) / (CSF PRE ALBUMIN+ALBUMIN) / (S ALBUMIN). It was found that the best index to appraise the behavior of IGG is: (CSF IGG/S IGG) / (CSF PRE ALBUMIN-f ALBUMIN/S ALBUMIN) that shows an average of 0.56 and a standard deviation of 0.32 in the material studied.