During 1981 a World Health Organization Study Group recommended that multibacillary (MB) leprosy patients should be given multidrug therapy (MDT) for at least 2 years and, wherever possible, until skin-smear negativity. This paper reports on the experience with MDT for MB patients under routine field conditions in the leprosy control program of the All Africa Leprosy and Rehabilitation Training Center (ALERT) in the Shoa Region of Ethiopia. The period of MDT to reach skin-smear negativity was evaluated for 348 new MB patients. Only 31.6% of these patients could be released after 26 four-weekly doses of MDT, and 19.8% needed over 5 years of MDT. The average period of MDT to reach skin-smear negativity was estimated at about 4 years. Of 3343 patients of cohorts which, almost exclusively, consisted of patients treated with dapsone before MDT, 72.8% were released after 26 four-weekly doses of MDT; whereas of 712 patients of cohorts which mainly included new patients, only 23.5% were released. It was estimated that if MDT would be stopped, regardless of skin-smear results, after 26 four-weekly doses of the drugs collected within a period of 3 years, about 80% of the patients would complete treatment. The operational problems with continuation of MDT until skin-smear negativity are discussed. Although as yet it has not been proven by study results that after 2 years of MDT the relapse rate will be low, the available knowledge indicates that this is likely to be the case. Based on a) probability, b) the finding that 2 years of MDT can be maintained in the majority of the patients, and c) the operational difficulties with the continuation of MDT until skin-smear negativity, it is recommended that MDT should be limited to 2 years. MDT of limited and fixed duration will facilitate the implementation and expansion of the treatment in parts of the world where most patients are not yet benefitting from this treatment.