Using inductively coupled argon plasma emission spectroscopy, we measured 19 trace elements in cerebrospinal fluid of 265 patients who were undergoing diagnostic lumbar puncture. Thirty-three patients had Alzheimer-type dementia (ATD); 16 patients had other dementing illnesses; and 20 had no neurologic disease. There were seven cases of autopsy-proven Alzheimer's disease (AD) and eight autopsy controls. We found elevated CSF silicon in 24% of ATD and 71% of AD patients. We found no relationship between CSF aluminum, arsenic, lead, or manganese and ATD, AD, or other dementing illnesses.