Maize with enhanced provitamin A carotenoids (biofortified), accomplished through conventional plant breeding, maintains vitamin A (VA) status in Mongolian gerbils (Meriones unguiculatus). Two studies in gerbils compared the VA value of beta-cryptoxanthin with beta-carotene. Study 1 (n 47)examined oil supplements and study 2 (n 46) used maize with enhanced beta-cryptoxanthin and beta-carotene. After 4 weeks' depletion, seven or six gerbils were killed; remaining gerbils were placed into weight-matched groups of 10. In study 1, daily supplements were cottonseed oil, and 35, 35 or 17.5 nmol VA (retinyl acetate), beta-cryptoxanthin or beta-carotene, respectively, for 3 weeks. In study 2, one group of gerbils was fed a 50% biofortified maize diet which contained 2.9 nmol beta-cryptoxanthin and 3.2 nmol beta-carotene/g feed. Other groups were given equivalent b-carotene or VA supplements based on prior-day intake from the biofortified maize or oil only for 4 weeks. In study 1, liver retinol was higher in the VA (0.74 (SD 0.11) micromol) and beta-cryptoxanthin (0.5 (SD 0.10) micromol) groups than in the beta-carotene (0.49 (SD 0.13) micromol) and control (0.41 (SD 0.16) micromol)groups (P<0.05). In study 2, the VA (1.17 (SD 0.19) micromol) and maize (0.71 (SD 0.18) micromol) groups had higher liver retinol than the control (0.42 (SD 0.16) micromol) group (P<0.05), whereas the beta-carotene (0.57 (SD 0.21) micromol) group did not. Bioconversion factors (i.e. 2.74 microg beta-cryptoxanthin and 2.4 microg beta-carotene equivalents in maize to 1 microg retinol) were lower than the Institute of Medicine values.