This study examined the relationship between maximal aerobic work capacity (maximal oxygen uptake, V̇O max) and two variables (occupational group and history of cattle herding) related to the behavior of the Ngisonyoka Turkana, a group of East African pastoralists maintaining a traditional herding lifestyle. Maximal oxygen uptake was measured for 19 men aged 20-44 years using a Monark bicycle ergometer. In line with previous reports for East Africans, there was little difference among mean V̇O max for three Ngisonyoka age groups (20-29, 30-39, 40-49 years), P > 0.05. However, V̇O max varied with history of cattle herding [defined as either (1) presently herding cattle, (2) had formerly herded cattle, or (3) had never herded cattle], P < 0.01. Maximal oxygen uptake also varied with occupational group (defined as junior herder, senior herder, herdowner [= former herder], or impoverished herdowner [= resumed herder]), P < 0.05. Thus, culturally defined work history and occupational group are positively associated with V̇O max, and may be useful in field studies of the effects of past and present activity levels on aerobic capacity. © 1994 Wiley-Liss, Inc.