Trophallaxis and feeding relationships in the eastern subterranean termite, Reticulitermes flavipes (Kollar), were examined using a novel marking technique, rabbit IgG protein coupled with an enzyme linked immunosorbent assay (ELISA) to detect the marker. Transfer experiments in small dishes evaluated the trophallactic transfer of the marker from donor workers fed IgG-treated paper to recipient workers or larvae. Worker donors rapidly acquired the marker, and 100% of donors tested positive within 24 h. Trophallactic transfer from donors to recipients was relatively inefficient, and 51 +/- 2% of recipient workers and 31 +/- 2% of recipient larvae tested positive at 72 h. Based on the mean optical density counts, approximately 27% of marker ingested by the donors was passed on to the recipient workers in the first 24 h, 14% to recipient larvae, and 26% to recipient soldiers. The ability of soldiers to feed independently of workers was examined in dish assays. Soldiers showed no significant uptake of the marker when isolated from the workers, and uptake increased significantly when workers were present. The distribution of the marker was further studied in larger colony fragments composed of workers, soldiers, nymphs, and larvae. Marker acquisition by the different castes/developmental stages was highly variable, with workers and nymphs acquiring the marker at a faster rate than soldiers and larvae. The results of this study contribute to our understanding of the foraging ecology and social behavior in R. flavipes. In addition, they may help design improved control programs for subterranean termites based on baits.