Systemic lupus erythematosus (SLE) frequently involves the central nervous system (CNS), but to a considerably lesser degree leads to peripheral neuropathy as measured by conventional nerve conduction velocity studies. Neuropathic symptoms are, however, frequently reported. Abnormalities of other nerve fibers than the large myelinated nerves might thus be responsible for such phenomena. Three age matched groups of 44 patients with SLE, 50 patients with rheumatoid arthritis (RA) and 45 healthy controls were investigated with quantitative sensory thermotesting. Warm detection thresholds (WDT) and heat pain detection thresholds (HPDT) were found significantly higher in SLE compared to RA and controls. There were no differences between the RA and the control group. In the SLE group no association to disease duration, medication or CNS abnormalities were found. Neuropathic symptoms and vibration thresholds showed weak associations to WDT. These findings imply that there is an impairment of C-fibre function in SLE. This small fibre neuropathy is probably not part of a generalized diffuse polyneuropathy also affecting large fibres, although this can not be ruled out completely by this study.