I observed leaping behavior in the white-faced saki (Pithecia pithecia) and the black-bearded saki (Chiropotes satanas satanas) for 15 and 10 months, respectively, as part of a larger study of positional behavior in the tribe Pitheciini. I used focal animal instantaneous sampling to observe the two species on separate islands in their natural habitat at Guri Lake, Venezuela. Leaping behavior correlates with patterns of forest use and body size, and differences between the species relate more to habitat preferences than to habitat differences per se. Pithecia usually chose vertical or highly angled supports of lower tree portions for take-off and landing, and took off from a stationary posture. Chiropotes took off from the main crown or terminal branches, gaining momentum from locomotor movement before performing a leaping take-off. Pithecia's vertical body orientation and longer leap distance allowed it to assume a mid-flight tuck to prepare for a hindlimb-first landing onto a solid support, and to absorb landing forces with its relatively longer hindlimbs. Chiropotes remained more pronograde throughout its leaps, and minimized landing forces by landing on all four limbs onto numerous flexible supports in the terminal branches. The smaller-bodied P. pithecia is specialized for vertical clinging and leaping, and exhibits behavioral and morphological parallels with other vertical clingers and leapers. The larger C. satanas is a generalized leaper that lacks morphological specializations for leaping. Pithecia's use of solid supports in the lower tree portions allows it to move quietly through the forest–one of a suite of behaviors related to predator avoidance. This example of variation within one behavioral category has implications for devising locomotor classifications and interpreting fossil remains. Am. J. Primatol. 66:369–387, 2005. © 2005 Wiley-Liss, Inc.