On 27 May 2007 I discovered two Brown-headed Cowbird (Molothrus ater) eggs in an artificial nest in a wooded fence line on the Tallgrass Prairie Preserve, Osage County, Oklahoma. The artificial nest was one of 20 placed along a transect 10 days earlier and baited with two infertile Blue Quail (Coturnix adansonii) eggs during a study on nest detection and predation. Brown-headed Cowbird parasitism of artificial open-cup nests in the absence of host nesting activity is rare, but has been reported. This occurrence of superparasitism represents the first record wherein more than one cowbird egg was deposited in an artificial nest, indicating that either a single female repeatedly parasitized the nest, or that a second female contributed an egg to the previously parasitized nest.