The effectiveness of microbial polymers in stabilizing soil aggregates varies among microbial strains. Our objective was to determine the ability of several microbial extracellular polymers to flocculate soil particles, stabilize soil structure, and improve water infiltration in diverse soil types. The effect of four bacteria strains (Azotobacter indicus, Arthrobacter viscosus, Chromobacterium violaceum, and Bacillus subtilus), two deuteromycete strains (Cryptococcus laurentii and Hansenula holstii), a reference compound (hydroxyethyl guar), and a high molecular weight polyacrylamide (PAM) on soil structure and water infiltration was investigated under laboratory conditions. Application of 1.0 mg C g-1 soil of any microbial polymer increased aggregate stability. Chromobacterium violaceum, Cryptococcus laurentii, and hydroxyethyl guar were the most effective in stabilizing soil aggregates (by 40-50%) when the soil was incubated for 4 weeks. Application of 100 mg L-1 of bacteria strains or hydroxyethyl guar in irrigation water increased cumulative water infiltration and the sorptivity coefficient. However, 100 mg L-1 of deuteromycete strains in water did not affect water infiltration and slightly decreased the sorptivity coefficent. Although application of 10 mg PAM L-1 increased soil flocculation, it greatly reduced (55%) water infiltration and the sorptivity coefficient in all soils tested.