Baby pigs were maintained in either a germ-free or a conventional environment and fed a sterile condensed milk diet (10 micrograms Fe/g milk solids) supplemented with 0, 50 or 100 micrograms Fe/g solids from FeSO4.7H2O or given an im injection of 100 mg Fe from Fe dextran. Pigs were reared on these diets for 4 wk, and weekly measures of gain, food consumption and hematology were taken. The pigs were then killed, and organ weights were taken and tissues analyzed for Fe concentration. All conventional pigs not given supplemental Fe died. None of the unsupplemented pigs raised in the germ-free environmental died. Conventional pigs gained faster and more efficiently and became anemic more rapidly. However, conventional and germ-free pigs were similar in the efficiency with which they incorporated supplemental Fe into hemoglobin or stored Fe in liver and spleen. We concluded from this study that both germ-free and conventional pigs fed a condensed milk diet require 50 to 100 micrograms Fe/g milk solids or more than 100 mg of Fe from Fe dextran once parenterally to maintain desirable hematological traits for 4 wk.