Symptomatic fatigue has not been investigated previously in a multiple sclerosis population. Potential subjects were the 78% of 656 individuals with multiple sclerosis who indicated in a previous study that they experienced symptomatic fatigue. Three hundred nine subjects (60%) returned a follow-up questionnaire on symptomatic fatigue. Ninety percent described fatigue as "tiredness or the need to rest," but 43% of them indicated that "sleepiness" was part of the symptomatology. In 48% fatigue made other MS symptoms worse. Fatigue tended to occur in the late afternoon and evening. It occurred almost daily for more than 66% of the subjects. In 47% of the subjects fatigue usually subsided within a few hours; in other subjects occurrences were of variable length (40%) or lasted between 6 and 24 hours (8%). Ninety percent said that fatigue was worse at warmer environmental temperatures. Fatigue was worse for 83% after "vigorous exercise" and for 64% after "moderate exercise" although 15% reported that moderate exercise helped to reduce fatigue. Meditation, some drugs, and cooling with water reduced fatigue in a majority of the small proportion of the population trying these techniques. A planned daily schedule of activity and rest seemed to be a partially effective response to symptomatic fatigue for the majority of subjects studied.