Insecticide resistance in the stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae), has been demonstrated previously, but mostly with insecticides that are no longer used, such as the organochlorines. Resistance to commonly used pyrethroids has been evaluated twice, but only in the midwestern United States. Stable fly susceptibility to a commonly used pyrethroid, permethrin, was determined in Florida to assess the possibility of resistance development. Diagnostic concentration evaluations of three stable fly field strains demonstrated a maximum of 57 and 21% survival to permethrin residues of 3× and 10× the LC₉₉ of a susceptible strain, respectively. Stable flies from an equine facility with no reported insecticide use demonstrated ≈20% survival with a 3× diagnostic concentration. Despite a distance of 91-km between field collection sites, survival profiles of field-collected stable fly strains were similar. Although an established stable fly colony collected from a local dairy previously expressed low level resistance to permethrin residues, five generations of laboratory permethrin selection increased resistance 15-fold.