Prolactin concentrations in avian plasma have been traditionally quantified using a radioimmunoassay (RIA) procedure. RIA is useful for such studies due to its sensitivity and specificity (e.g., Follett et al. 1972, Wingfield and Farner 1975, McNeilly et al. 1978, Burke and Papkoff 1980, Schwabl 1993). For example, the heterologous RIA for detecting prolactin in turkeys, developed by McNeilly et al. (1978), recovered 98% of a prolactin standard added to a turkey plasma sample and exhibited less than 0.1% cross reactivity with other plasma hormones. In an homologous RIA developed by Burke and Papkoff (1980), detection limits of approximately 0.42 ± 0.13 ng were reported. Despite these advantages, RIA has drawbacks for field ecologists, including the high cost of isotope and the necessity of working with radioactive ligands. We report here a non-radioactive alternative to RIA for measurement of plasma prolactin levels in the House Wren (Troglodytesa edon L.), namely, a commercially-available (Leinco Technologies Inc.) enzyme-linked immunosorbant assay (ELISA) kit. The ELISA kit used was based on capturing avian plasma prolactin with a murine monoclonal antibody (mAb) specific for prolactin, followed by detection of the captured prolactin with a polyclonal antibody directed against prolactin. The test may be ideal for usage by field ecologists since it is non-isotopic, portable, does not rely on specificity of the detection antibody, quick, involves little sample or standard preparation, can be used on small sample volumes and requires little specialized equipment.