This is a prospective study, with 55 patients in coma, in which wasn't chosen sex, age, intensity of coma or etiology. It was measured the concentration of the potassium and the sodium in cerebrospinal fluid, (CSF) and in the serum, to find an auxiliary way to value the prognostic. It is know that the potassium in the CSF is extremely stable, and it mantains the tax without alterations, even when the potassium in CSF is rapid and intensity raised after death. Experimental studies show the potassium raised in CSF in serious damaged brain. Our results show, in patients who recovered consciousness, normal values (means 2,61 mEq/1) of potassium in CSF. The mean of values of potassium in CSF in the group of patients who had bad evolution (they died) show index estatisticaly up of normal values (2,97 mEq/1) and this shows a serious damaged brain and/or irreversible, able to affect the stability of CSF potassium. These index are present in some kind of coma or etiology, showing that raised potassium in CSF, indicates bad prognostic, in some kind of coma. With the sodium, the results show that this ion don't serve to this finality, because its concentrations ins't stable in CSF, and change with the blood alterations of natremia.