Two methods for collecting specimens for measuring sequential antibody activity of infectious bronchitis virus (IBV) were compared. Whole blood was collected on filter-paper strips, dried for 2 hr at 37 C, and then stored in plastic bags at 4 C or eluted overnight and tested immediately. Eluates of whole blood were paired with serum samples and tested for IBV antibody activity by enzyme-linked immunosorbent assay (ELISA) at four weekly intervals. Both sampling methods yielded ELISA antibody levels that were detectable at 7 days postinfection (PI), peaked at 21 days PI, and then began to decline by 28 days PI. The paired samples showed no significant difference (P less than 0.05) between ELISA titers at any time tested. Whole blood dried on filter paper could be stored sealed in plastic bags at 4 C for at least 2 weeks with no appreciable loss of antibody titers. Virus-neutralizing antibodies, measured in serum only, were not detectable until 14 days PI but then continued to rise through 28 days PI. It was concluded that eluates of whole blood dried on filter paper may be used as an alternative to sera in ELISA for measuring IBV antibodies.