Giant anteaters (Myrmecophaga tridactyla) are among those mammals for which a particularly low metabolism has been reported. In order to verify presumably low requirements for energy, we used 8 captive adult anteaters (2 males, 6 females; aged 1-14 years; body mass between 46-64 kg) in a total of 64 individual experiments, in which a variety of intake levels was achieved on a variety of diets. Digestible energy (DE) intake was quantified by measuring food intake and faecal excretion and analyzing representative samples of gross energy, and animals were weighed regularly. Maintenance DE requirements were calculated by regression analysis for the DE intake that corresponded to no weight change; this resulted in an estimate of 347 kJ DE kg-0.75d-1, which is low compared to the 460-580 kJ DE kg-0.75 d-1 maintenance requirements of domestic dogs. In theory, metabolic requirements below the mammalian average could make species particularly susceptible to overfeeding, if amounts considered adequate for other mammals are given. Anecdotal reports on comparatively fast growth rates and high body masses in captive as compared to freeranging giant anteaters suggest that feeding regimes in captivity should be further assessed.