For many patients with Parkinson disease and levodopa-related motor fluctuations, the latency to onset of action of a single dose of a levodopa preparation may be both long and variable. In an effort to find a more rapidly acting and reliable preparation of levodopa, we therefore studied the efficacy of single doses of an oral solution of 250 mg of levodopa methyl ester (ME) with benserazide, 50 mg and of a molar equivalent dose of dispersible Madopar (DM) (50/200) in 13 patients in the fasting state after overnight drug withdrawal. The response of seven of these patients was compared to that after two Sinemet 25/100. The latency to "on" was equally fast with ME and DM, and significantly faster than after standard Sinemet. The duration of "on" was similar with all three. Because of this more rapid relief of "off" periods, both ME and DM offer a potential clinical advantage over standard preparations of levodopa.