Progressive systemic sclerosis (PSS) is a systemic disease with a high frequency of gastro-intestinal involvement. The present thesis deals with the occurrence of, the complications to, and the treatment of the esophageal manifestations combined with more experimental studies on small intestine manifestations. The conclusions in this thesis are based on results achieved in 9 original previously published papers. The pattern of esophageal dysmotility is thoroughly evaluated in 156 consecutive PSS patients and is found to be identical to what is found in other large series of PSS patients. In paper no. I dysmotility variables are correlated to the occurrence of gastroesophageal reflux (GER) and it is shown that also in this group of patients with well defined dysmotility problems the only reliable GER test is pH-metry. Esophageal dysmotility furthers esophageal candidosis, which is further facilitated by anti-reflux treatment. This problem is evaluated in paper no. V. Progression of esophageal dysmotility in spite of D-penicillamine treatment is shown in paper no. VII and confirms the non-stable condition of the PSS patient in regard to esophageal manifestations and complications. This point is also outlined in paper no. IX concerning surveillance and continuous treatment of esophageal PSS. Esophageal stricturing is a well-known entity in PSS. The etiologic question of esophageal stricturing being a manifestation of PSS and/or a peptic complication, is approached in paper no. VIII. PSS manifestations of the small intestine are not as frequent as in the esophagus, in the present material only 19% presented with X-ray changes. However, bacterial count of duodenal juice as an indirect measurement of small intestinal dysmotility in paper no. VI indicates a much larger percentage of small intestinal involvement than revealed by X-ray. In paper no. VI the exocrine pancreatic function was assessed in 16 PSS patients. It is shown that the endogenous stimulation capacity is preserved even in spite of demonstrable small intestinal PSS involvement and that exocrine pancreatic function is frequently reduced, but rarely to a degree of clinical significance. Small intestinal enterocyte function is evaluated according to the ability to hydrolyse folatepolyglutamates and to absorb D-penicillamine, and is in both respects found less than normal. In an ultrastructural evaluation (paper II) the enterocytes presented signs of defective fat transport. PSS manifestations of the gastrointestinal tract are frequent and burdensome to the patient. Omeprazole and new prokinetic drugs have rendered new therapeutic potentialities, which, however, more than ever demand constant surveillance and individualized regulation of treatment.