Ct values of DNA extracted from airborne conidia of F. circinatum were estimated by real-time PCR of a fragment of the IGS region. Environmental samples were collected from spore traps in San Francisco (site I; June 2002, boldface open circle; July 2002, filled circle; October 2002, lightface open circle) and San Bruno (site II; June 2002, dotted diamond; July 2002, filled diamond; October 2002, bisected diamond), Calif. Standardization was done with DNA extracted from spores of F. circinatum NRRL 25331.