Thirty-nine consecutive patients with recent-onset rheumatoid or psoriatic arthritis were randomly allotted for six months period either to the experimental progressive dynamic strength training group (EG, 10 women and 11 men; 41 +/- 10 yrs), or to the control group (CG, 10 women and 8 men; 45 +/- 11 yrs) who just maintained their habitual physical activities. All patients received antirheumatic medication throughout the experimental period. During the study period significant improvements took place in the EG in maximal muscle strength of all examined muscle groups (31.5% for the knee extensors, p < 0.001; 14.8% and 10.7% for the trunk flexors and extensors, p < 0.01; 27.8% and 20.4% for grip strength, p < 0.001) as well as in erytrocyte sedimentation rate (p < 0.05). Ritchie's articular index (RI) (p < 0.001) and HAQ (p < 0.01). In the CG only the decrease in RI was statistically significant (p < 0.05). Erosive changes in joints increased only slightly and less in the EG than in the CG. The present results suggest that dynamic strength training in early arthritis increases the neuromuscular performance without detrimental effects on disease activity or joint damage.