Hybrid zones between races and semispecies hold considerable interest for evolutionary biology. They may be examined in regard to the selection pressures that adapt each population to its geographic range (Blair, 1943). The width and age of the hybrid zone and the mechanisms which restrict gene flow across it are of particular relevance to understanding the origin and evolution of ethological isolating mechanisms. This paper considers three narrow hybrid zones between the iguanid lizards Sceloporus woodi and S. u. undulatus. Sceloporus woodi is normally restricted to the sand-pine scrub association of the Florida peninsula. S. u. undulatus inhabits dry, open forests in the southeastern United States; in Florida it is most abundant in the longleaf-pine/turkey-oak association (hereafter termed sandhill vegetation). Laessle (1942) defined these associations, and the striking differences in physiognomy between them have been detailed (Laessle, 1958). The overstory of sand-pine scrub consists only of Pinus clausa. The understory is a dense thicket of evergreen sclerophyllous shrubs and is dominated by oaks which range in height from one-half to two meters. The ground surface is a mosaic of bare sand and thin, but well-compacted, leaf litter over which herbaceous growth is extremely sparse. Pinus palustris was the dominant tree in primeval sandhill vegetation, and Quercus laevis was both less common and lower in height. However, logging and fire control have favored Quercus, and it is presently the more abundant tree in most stands of sandhill vegetation. In contrast to sandpine scrub, shrubs are few and scattered while herbaceous ground cover is welldeveloped. The herbaceous layer, composed mainly of wiregrasses (Aristida; Sporobolus) but with many species of forbs, combines with fallen pine needles and oak leaves and forms a loose cushion that varies in depth depending on the recency of ground fire. The associations are frequently adjacent, and the transition between them usually takes place within only a few meters; in some places, one can stand in both associations simultaneously. The three hybrid zones studied are along ecotones in the Ocala National Forest. The Lake Eaton ecotone is near the intersection of FS-79A and FS-96 about 0.5 miles south of Lake Eaton (Section 26, T. 14 S., R. 24 E.). The Forts Bear Hole ecotone is south of FS-95 about 1.5 miles southwest of Forts Bear Hole (Sections 17 and 18, T. 16 S., R. 25 E.). The Alexander Springs ecotone parallels SR-445 0.3 miles to its west and about 2.0 miles southwest of Alexander Springs.