In 12 patients with amyotrophic lateral sclerosis (ALS) participating in a therapeutic trial with intrathecally applied human fibroblast interferon-beta (IFN-beta) and in 9 untreated ALS patients, we found significantly elevated circulating serum IgG immune complexes (CIC), quantitative immunoglobulin changes, and creatine kinase (CK) elevation; CK reached significantly more often pathological levels in non-bulbar disease. Dermal ultrastructural changes were equally present in all treated as well as untreated ALS patients. Some time ago IL-6 was quantitatively cleaned out of the Fiblaferon-preparation. Erythrocyte sedimentation rate (ESR) rose during intrathecal IFN therapy in 9/10 ALS patients. In 4/4 adequately monitored motoneuron patients, this elevation coincided with a decrease of serum CK, while ESR and CK did not correlate in 60 non-ALS non-IFN neurological controls. Collagen ultrastructure, CSF total protein or barrier function, immune complexes, immunoglobulin quantitation and serum CK may contribute to differentiated diagnosis and should be included in future study protocols.