Thirty-four patients with idiopathic fluctuating Parkinson's disease and early afternoon "delayed on" or severely resistant "off" periods, in spite of long-term antiparkinsonian therapy, were studied. The first afternoon levodopa administration was substituted with an equimolar dosage of the liquid formulation levodopa methyl ester (LDME). The major end-points for efficacy were latency to "on" and duration of "on" periods. The patients were divided into five subgroups according to their baseline treatment and they were evaluated monthly for 6 months using the Unified Parkinson's Disease Rating Scale. The patients completed weekly self-evaluation using an "on-off" chart. LDME was well tolerated by all the patients. A statistically significant reduction in latency to "on" was observed in all patients. The clinical effect of LDME remained stable during the treatment period (repeat measures ANOVA). The more rapid clinical effect of LDME and its stable and predictable antiparkinsonian activity represents a new and useful approach for treating patients with complicated Parkinson's disease.