In studies of Guillain-Barré syndrome, functional deficit is usually assessed according to a functional scale consisting of several categories. The level of interobserver agreement in this scoring method is not known; furthermore, this method seems to be insensitive when applied to bedridden and artificially ventilated patients. We have developed an additional score (MRC-sumscore), reflecting muscle strength in general. Both scoring methods, tested in Guillain-Barré patients, have an almost perfect interobserver agreement. For the functional score kappa = 0.85, and for the MRC-sumscore r2 = 0.96. The MRC-sumscore is easily assessed and more sensitive than the functional score when patients are bedridden or artificially ventilated.