The effect of two levels of dietary protein and exercise on iron metabolism in pregnant Sprague-Dawley rats was studied. Animals were assigned to the following diet and exercise groups on the first day of gestation: high protein sedentary (HS), high protein exercise (HEx), low protein sedentary (LS), low protien exercise (LEx). Animals in the exercise groups swam continuously for 75 minuites the first day and 90 minutes daily thereafter, throughout the study. Hemoglobin, hematocrit, liver iron concentration and spleen iron concentration were measured at day 0, 3, 6, 9, 12, 15, 18, and 21 of gestation. Mean hemoglobin, hematocrit and liver iron concentration values were lower at day 21 than at day 0 of gestation. Mean hematocrit and hemoglobin for the LEx group were the lowest for days 9 through 15. At day 15 the mean hematocrit for the LEx group was significantly (p < 0.05) lower than that of the other groups. The HEx group had the highest hematocrit and hemoglobin values at day 21 of gestation; hemoglobin was significantly (p < 0.05) higher. No difference in mean spleen iron concentration from day 0 to day 21 was found, however, the low protein groups had higher spleen iron values early in pregnancy that the high protein groups. The mean spleen iron concentration of the LEx group was significantly (p < 0.05) higher than those of the HS and HEx groups at day 6. A trend for higher liver iron concentration values of the low protein groups than high protein groups was also observed. The LEx group had a significantly (p <0.05) higher mean liver iron concentration at day 18 than the other groups. Both protein nutriture and exercise appear to affect iron metabolism in pregnant rats. / M.S.