Several studies have shown the effects of the mounds of the banner-tailed kangaroo rat (Dipodomys spectabilis Merriam) on desert annuals. There can be effects on density, biomass and composition of the herbaceous assemblage (Moroka et al., 1982; Mun & Whitford, 1989). As a result of a long-term study of a site in south-eastern Arizona, we observed a positive effect of these mounds on the growth, flowering and fruiting, and survival of creosotebush, which is the dominant woody perennial of the community. This effect became obvious at this site long after the kangaroo rats disapppeared from the system, probably as a result of invasion of creosotebushes and other shrubby vegetaion into what was previously a desert grassland system. Whereas creosotebushes had a negative effect on the kangaroo rat population, the mounds created by these rodents have had a residual positive effect on the creosotebushes. A number of measurements were made to examine the nature of this unusual, if not unique, relationship, and to provide some basis for speculation as to the cause(s) of the positive effect.