Nine strains of a new arbovirus have been isolated from the ticks Dermacentor variabilis and Haemaphysalis leporispalustris collected in the Tampa Bay area of Florida. It has been named Sawgrass virus. The virus passes a 0.22 µ Millipore filter, is sensitive to sodium deoxycholate, and is probably a ribonucleic acid virus. No antigenic relation has been shown with 23 other tick viruses nor with representatives of other viruses as shown by tests with antiserum to 50 other arboviruses. Tacaribe and Tamiami viruses. and eight common murine viruses. Significant neutralizing-antibody levels were not found in the serum of small animals collected in the areas from which the animals harboring infected ticks were collected, nor in a small sample of human serum collected from persons considered at high risk.