Sepsis-induced skeletal muscle protein catabolism may be mediated by systemic TNF-α.Immune cell TNF-α production is well recognised, but recent studies suggest that TNF-α may also be present in muscle (Saghizadeh et al, 1996). We tested the hypothesis that in-vivo endotoxaemia would induce TNF-α gene expression in human skeletal muscle. In this Local Research Ethics Committee-approved study 8 healthy male volunteers, mean (SD) age 32.0 (4.4) yr were examined twice, in random order and 2 weeks apart. On one occasion they received 4ng/kg i.v E.coli lipopolysaccharide (LPS), and on the other the same volume of i.v sterile normal saline. Automated pulse rate, rectal temperature and oxygen consumption ₂), and arterialised venous plasma concentrations of cortisol, IL-6 and TNF-α were measured hourly, for one hour before and 6 hours following i.v LPS/saline. Percutaneous quadriceps femoris biopsies were obtained (conchotome technique) immediately prior to LPS, and 6 hours after i.v LPS/saline. Tissue samples were immediately fixed in neutral formalin, later processed into paraffin wax and 7 micron sections cut and mounted onto silicon-based glue-coated slides, for in-situ hybridisation. This employed an S³⁵-labelled cDNA probe to TNF-α,with autoradiographic product disclosure. TNF-α label was manually semi-quantitated thrice by one blinded examiner (score 0-3 for grain count per cell, and 0-3 for % of cells positive for grain). Statistical comparisons of the systemic effects of LPS used repeated measures ANOVA and, where treatment/time interactions were apparent, with post-hoc Student’s t-test using Bonferroni corrections for multiple comparisons. LPS caused fever, tachycardia and marked increases in plasma cortisol, IL-6 and TNF-α concentrations (saline/LPS comparisons made at peak LPS-induced change): pulse rate 64.4 (8.8) vs 90.6 (10.3) bpm, core temperature 36.4 (0.2) vs 37.8 (0.3) °C, VO₂ 120.2 (8.3) vs 145.9 (18.7) ml/min/m²,cortisol 159.8 (46.6) vs 721.6 (105.6) nmol/L, IL-6 11.0 (8.7) vs 1074.0 (754.9) pg/mL and TNF-α 13.9 7.7) vs 960.7 (589.6) pg/mL, p<0.01 for each comparison. Tissue TNF-α label was present at similar levels before LPS and after saline, mean scores 1.44 (0.81) and 1.39 (0.63) respectively, but increased to mean score 2.03 (1.13) following LPS. TNF appears to be constitutively expressed in human skeletal muscle, and may be inducible by systemic LPS. This suggests that local induction of TNF-α may be important in skeletal muscle metabolic responses to endotoxaemia.