Serum antibody responses to shigella lipopolysaccharide (LPS) and invasion plasmid-coded antigens (Ipa) were studied in 74 Swedish patients with culture verified bacillary dysentery using class-specific enzyme immunoassay (EIA). Anti-LPS responses were found in 80% and 79% serum samples, respectively, from S. flexneri and S. sonnei infected patients and anti-Ipa responses in 60% and 43%, respectively. The mean anti-Ipa IgG antibody titres in S. flexneri infected patients remained high for 4-6 months after onset while the anti-LPS IgG antibody titres had dropped to normal levels. The specificity of EIA for shigella Ipa was 90% and for S. dysenteriae, S. flexneri and S. sonnei LPSs it varied between 84% and 90%. No close correlations between the anti-LPS and anti-Ipa antibody responses were observed indicating that they may be differently regulated. The dynamics of the serum antibody responses indicates that an anti-LPS response is a good indicator of a recent shigella infection and an anti-Ipa IgG response a good indicator of a previous infection.