The purpose of this research was to identify the factors which people with rheumatoid arthritis (RA) believed contributed to their fatigue. A second purpose was to examine the relationships among identified factors and the sensation of fatigue. One hundred people with RA were asked to identify verbally factors which they believed contributed to their fatigue. The three most frequently identified factors included RA disease activity, disturbed sleep and increased physical effort. These factors were operationalized and measured as joint pain using the Modified McGill Pain Inventory, fragmented sleep through overnight electroencephalographic (EEG) sleep studies, and reduced physical ability using walking time and grip strength measures. Fifteen of the original subjects with RA and 12 age and gender matched control subjects completed the second phase of the research. Five of the RA subjects were experiencing a disease flare while the remaining 10 were either in remission or their disease was midly active. Those subjects in flare had significantly (P less than 0.01) more joint pain, significantly (P less than 0.05) more fragmented sleep, and significantly reduced functional capacity as measured through walking time (P less than 0.05) and grip strength (P less than 0.05) when compared to non-flare and control subjects. Fatigue levels of the subjects in flare were positively correlated with joint pain (r = 0.62), fragmented sleep (r = 0.42) and grip strength of the right hand (r = 0.52) and left hand (r = 0.88). Fatigue levels of non-flare and control subjects were negatively correlated with the majority of measured variables.(ABSTRACT TRUNCATED AT 250 WORDS)