In chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), the acute motor response following withdrawal and reestablishment of intravenous immunoglobulin (IVIG) therapy was studied. In a prospectively designed case series 11 CIDP patients in IVIG maintenance therapy were assessed with isokinetic dynamometry, nerve conduction studies, and functional tests. After short-term withdrawal of IVIG, eight treatment-responsive patients had a 14.2% (8.6-20.0) loss of isokinetic strength of 12 muscle groups. Three patients remained stable without treatment and were excluded from further study. On days 5 and 10 after reinitiation of IVIG therapy isokinetic muscle strength increased by 5.5% (1.6-9.6) and 11.9% (7.5-16.5), respectively, but there was no further increase at day 15. Improvement of walking velocity and hand function coincided. The minimal F-wave latency shortened, whereas other electrophysiological parameters remained unchanged. In conclusion, isokinetic dynamometry is a sensitive and clinically relevant method for monitoring the acute response to IVIG treatment in CIDP.