AIM:To evaluate the prevalence of Giardia lamblia(G.lamblia)infection in patients with irritable bowel syndrome(IBS)and dyspepsia and to establish which is the mostaccurate test to diagnose the infection in this setting.METHODS:One hundred and thirty-seven patients whoconsecutively attended the Outpatient GastroenterologyClinic for the first time between January 2002 and De-cember 2003 due to symptoms of IBS and/or dyspepsiawere recruited.All patients underwent clinical evaluation,first-step haematology and chemistry tests,serologic as-says for celiac disease,lactose-H2 breath test,abdominalultrasonography,and esophagogastroduodenoscopy.Helicobacter pylori status was evaluated.In patients withsymptoms of IBS older than 45 years,colonoscopy wasalso performed.In all patients,duodenal biopsies andstool samples were examined for trophozoites and cystsof G.lamblia by several methods.RESULTS:G.lamblia was identified in 9 patients.Thefollowing diagnoses were also made:IBS(100/137,73%),functional dyspepsia(62/137,45%),organicdyspepsia(33/137,24%),and lactose intolerance(75/137,55%).A significant association was foundbetween giardiasis and H pylori infection(X~2=6.632,OR=12.4,CI=1.5-68.1).There were no symptomsthat reliably allowed the recognition of giardiasis.Direct search of the parasite in duodenal biopsy andstool sample examinations gave concordant results inall cases while histological examination of duodenal biopsies displayed a low sensitivity(e.g.,22.2%).CONCLUSION:In this consecutive series,diagnosisof G.lamblia infection accounted for 6.5% of patientswith IBS and dyspepsia.Duodenal biopsies for diag-nosis of giardiasis may be unnecessary if stool sampleexamination is performed. AIM: To evaluate the prevalence of Giardia lamblia (G. lamblia) infection in patients with irritable bowel syndrome (IBS) and dyspepsia and to establish which is the mostaccurate test to diagnose the infection in this setting. METHODS: One hundred and thirty-seven Patients whoconsecutively attended the Outpatient GastroenterologyClinic for the first time between January 2002 and De-cember 2003 due to symptoms of IBS and / or dyspepsia were recruited. All patients underwent clinical evaluation, first-step haematology and chemistry tests, serologic as-says for celiac disease , lactose-H2 breath test, abdominalultrasonography, and esophagogastroduodenoscopy .Helicobacter pylori status was evaluated.In patients with symptoms of IBS older than 45 years, colonoscopy wasalso performed.In all patients, duodenal biopsies andstool samples were examined for trophozoites and cystsof G.lamblia by Several methods .RESULTS: G.lamblia was identified in 9 patients. FOLLOWING diagnoses were also made: IBS (100/137, 73%), functio nal dyspepsia (62/137, 45%), organicdyspepsia (33/137, 24%), and lactose intolerance (75/137, 55%). A significant association was found between giardiasis and H pylori infection (X 2 = 6.632, OR = 12.4, CI = 1.5-68.1) .There were no symptom sure enough the recognition of giardiasis. Direct search of the parasite in duodenal biopsy andstool sample examinations gave concordant results inall cases while histological examination of duodenal biopsies displayed a low sensitivity (eg , 22.2%). CONCLUSION: In this consecutive series, diagnosisof G.lamblia infection accounted for 6.5% of patients with IBS and dyspepsia. Duodenal biopsies for diag-nosis of giardiasis may be unnecessary if stool sample introduction is performed.