Cocci coated with IgG, IgA and IgM occurred in 21, 20 and 9 of 28 urine specimens, respectively, containing Staphylococcus saprophyticus. There was no correlation between the occurrence of antibody-coated cocci and symptoms from the upper or lower urinary tract. Nor was antibody-coating correlated to the occurrence of proteinuria or haematuria. Antibody-coated cocci occurred more often, however, in patients with symptoms for 7 days or more than in patients with symptoms for a shorter duration. Direct haemagglutination of sheep erythrocytes was demonstrated in 30 of 61 washed urine sediments containing S. saprophyticus. There was a significant correlation between non-haemagglutinating specimens and the occurrence of antibody-coated bacteria in these specimens.