The signal intensity of cerebrospinal fluid (CSF) was studied by measuring the intensity of nine samples of CSF using various routine pulse sequences with 1.0 T and 0.1 T magnetic resonance imagers. The observed signal intensity differences between the CSF samples were small, as were the differences between the CSF samples and distilled water, although two of the samples were pathological with an elevated protein content. Signal intensity did not correlate with the protein content, and the location of the sample in the coil (head coils were used) caused more variation in the results than did the composition of the sample. The same results were obtained with both imagers. Our results suggest that CSF may be suitable for an intensity reference in routine patient studies in regions where the flow and pulsatile movement of CSF are slow enough not to affect the signal intensity, but further studies are needed to determine such regions in the CSF system.