A profiling ELISA was developed to detect antibody to the non-structural (NS) proteins Lb, 2C, 3A, 3D, and the polyprotein 3ABC, of foot-and-mouth disease virus (FMDV). The assay was used to examine panels of sem from naive cattle, and from experimentally infected or vaccinated animals. All sera front cattle experimentally infected with arty of the seven serotypes of FMDV were positive for antibody to 2C, 3A, 3D and 3ABC, and the majority were positive for Lb, The three categories of sera could be differentiated on the basis of the presence or absence of antibody, to the structural and/or NS proteins of FMDV. The assay is simple, rapid and reproducible and can be used to identify preview infection in animals which are seropositive for antibody to the structural proteins of the virus. Validating the assay with field sera demonstrated that antibody to 3ABC, and usually one or more of the other non-structural proteins, was detected only in animals reported to have shown clinical signs of FMD. Vaccinated cattle which had received less than five vaccinations, were frequently positive for antibody to 30 but were negative for antibody to 3ABC, Occasional animals which had received more than ten vaccinations had NS protein antibody profiles which were similar to those seen following infection. (C) 1998 Elsevier Science Ltd. All rights reserved.