Twenty-four patients with proven systemic sclerosis and with symptoms suggestive of malabsorption (i.e. chronic diarrhoea and weight loss) were investigated for small bowel bacterial overgrowth. Of the patients selected, six were suffering from the diffuse form of the disease. Jejunal aspiration was performed in all patients, and in nine normal volunteers. A specially designed double-lumen sterile catheter was used for this purpose and was introduced via a gastroscope. Twenty of these patients underwent a glucose hydrogen breath test. Eight patients (33%) had significant bacterial counts: > 10(5) colony forming units per ml (cfu/ml) of jejunal fluid. Less than 10(2) cfu/ml were found in the jejunal fluid from the nine control subjects. Glucose hydrogen breath testing was positive in seven patients, all of whom had significant jejunal bacterial growth. Diarrhoea rather than weight loss was shown to be the symptom which correlated best with the presence of bacterial overgrowth. Ciprofloxacin was used in six patients whose diarrhoeal symptoms ceased dramatically within 48 h of commencing the antibiotic. Trimethoprim produced a partial response despite bacterial sensitivity. A disadvantage of the hydrogen breath test is that subsequent antibacterial therapy cannot be specific, as bacterial species, antibiotic sensitivity and resistance are unknown. Systemic sclerosis involving the small intestine in the past has been said to more prevalent in patients with diffuse disease, whereas this study showed a preponderance of patients with long-standing limited cutaneous systemic sclerosis and small bowel involvement.