The Brief Repeatable Battery of Neuropsychological Tests (BRB-N) for MS consisting of the selective reminding, 10/36 spatial recall, symbol digit modalities, paced auditory serial addition (PASAT) and word list generation tests is a sensitive measure of early cognitive impairment in MS patients. We administered it to 19 chronic stable MS patients every 60 days for 120 days to examine variability. The mean coefficient of variation for the tests ranged from 18% to 22%. A significant practice effect was seen in the PASAT results (P < 0.05) using the Wilcoxon signed rank test. These results suggest that cognitive fluctuations analogous to motor fluctuations may occur in MS patients and that the BRB-N may be useful in clinical trials of agents expected to alter cognitive function in MS patients if test-retest variability and practice effects are taken into account. Further study is warranted.