In consecutive samples submitted to a clinical microbiology laboratory 22 out of 99 from outpatients and 23 out of 51 from inpatients yielded Klebsiella sp. A clinical reassessment of outpatients with ankylosing spondylitis (AS) and rheumatoid arthritis (RA) who had not been inpatients within the last year was made for disease activity and drug requirements. 124 patients with AS and 92 with RA were requested at assessment to submit a stool specimen for klebsiella examination, this being carried out without disclosure of the patient's clinical category. Two months later a questionnaire on symptom changes was collected and the results correlated with klebsiella carriage. Eighty-nine patients with AS and 82 patients with RA fulfilled all criteria for assessment. Of those assessed, 24 out of 89 AS patients and 26 out of 82 RA patients had klebsiella in the faeces. There was no correlation betweeh the initial clinical assessment category and klebsiella carriage. Seventy patients with AS and 57 paients with RA had no change in symptoms over the 2-month period. Nineteen AS patients and 31 RA patients noted symptom improvement or worsening. Of these, 3 AS and 10 RA patients had klebsiella in their faeces. There was no correlation between worsening of symptoms over a 2-month period and klebsiella carriage at initial assessment.