The use of sheep wool as a nesting material was examined from 1969 through 1975 on the island of Hawaii. Of the 10 bird species studied, six used wool in their nests. Both intro- duced and endemic birds use wool, with a significantly greater usage by endemic birds. Use of wool in nests appears correlated with the intricacy of a species' nest, with significant differences between degree of usage in complex and simple nests. Roughly built nests, like those of the Cardinal (Cardinalis cardinalis), contained no wool whereas the complex nests of the Elepaio (Chasiempis sandwichensis) had a great deal of it. Birds apparently use wool because of its ready availability and its binding quality. They gathered it from tufts that snag on branches as the sheep pass or from dried skins. The amount of wool in each nest varied both interspecifically and intraspecifically, but in all nests only the body contained wool; the lining was always of other material. A separate study compared an area void of sheep and an adjacent one containing sheep to deter- mine if wool is a preferred and sought-after material. Only the Elepaio was found consistently to travel distances to procure it; the other species used it only when available within their territories.- Department of Zoology, University of Hawaii, Honolulu, Hawaii 96822. Accepted 9 December 1975.