Ticks are bloodsucking parasites that are often found in tall grass and brush. There are more than 850 species of ticks worldwide; at least 100 can transmit more than 65 diseases,Both the Argasid and the Ixodid ticks to people, pets, cattle, sheep, goats and other livestock. Many domestic and wild animals are killed by tick–borne diseases. A nested polymerase chain reaction specific for Ehrlichia chaffeensis was used to attempt to amplify DNA from extracts of 100 individual ticks collected from 13 countries in central Missouri. Seventeen of 59 Amblyomma americanum and six of 41 Dermacentor variabilis ticks exhibited the characteristic 389– basepair product. This supports the hypothesis that these tick species may be vectors of human monocytic ehrlichiosis.