A serovar-specific antibody response to Ureaplasma urealyticum was observed in stillborns, neonates, and mothers by means of the modified metabolic inhibition test. Elevated levels of ureaplasma antibody were found in cases of stillbirth and neonatal respiratory disease. There was a higher risk of mortality among neonates with respiratory disease who had elevated levels of ureaplasma antibody. IgG and IgM serovar-specific antibody responses to U. urealyticum serovars were confirmed by the immunoperoxidase and immunofluorescence assays. In contrast to ELISA-based assays that use soluble membrane proteins as antigen, these three assays use whole intact cells. These observations suggest that the serovar-specific antibody response may be associated with the ureaplasma extramembranous carbohydrate (lypoglycan) coat, which comes off during centrifugation. With the immunoperoxidase assay, a heel-prick blood sample (20 microL) can be screened for 16 IgM or IgG + IgM + IgA (combined) responses in 4 hours. The predictive value of IgM antibody for U. urealyticum infection and other mycoplasma infections and for the risk of stillbirth and development of chronic lung disease should now be assessed.