In order to determine the pathogenic responsibility of Escherichia coli adhesins (ADHs) in urinary infections (UI), 2,000 different patients suffering different clinical urinary and male sexual gland infections were monitored. The ADHs were determined by agglutination techniques with human and guinea-pig red blood cells, Candida albicans and Saccharomyces cerevisiae cells and latex sensitized with GAL-GAL. In uncomplicated UIs, the possession of ADH is the main invasion mechanism for E. coli. The rate of E. coli ADH strains is very high (89%) in acute cases (727 of 818 cases: 310 of 362 cystitis; 104 of 113 recidivant cystitis; 120 of 126 pyelonephritis; 158 of 173 prostatitis, and 34 of 43 orchiepididymitis) and rare (10%) in asymptomatic or chronic cases (24 of 235 cases: 14 of 148 bacteriurias; 8 of 74 prostatitis, and 2 of 13 orchiepididymitis). A close relation is established between the presence of ADH and clinical symptoms. 90% (218 of 242) of acute cases with systemic symptoms are due to MR-type ADH strains, especially the P subtype. 71% (409 of 576) of acute cases with local symptoms are due to MS-type ADH strains. In complicated UIs the expression of ADH is not an essential condition for the invasion of the urinary apparatus. It has been strongly suggested that males are significantly more resistant to UI, both in the tract and parenchyma, than women. It can be deduced that the underlying disease is more liable to UI the lower the adherence level shown by isolated strains. Thus catheters, reflux and neurogenic bladder are, by far, more aggressive alterations than the prostatic adenoma, vesical tumor or lithiasis.