The average dietary selenium intake in Finland is naturally low, approximately 30 micrograms/d, when domestic grain is exclusively consumed. Selenium concentrations were determined in 46 individual breast milk samples collected after 1, 2, and 3 months of lactation in 1980, when the average Finnish dietary selenium intake was approximately 50 micrograms/d due to consumption of high selenium US grain. Selenium concentrations were characterized by a pattern of slight decline with advancing stages of lactation: 11.8 +/- 1.7 micrograms/l (n = 13), 10.9 +/- 1.9 micrograms/l (n = 18) and 10.0 +/- 1.9 micrograms/l (n = 15) at 1, 2 and 3 months post partum, respectively. This pattern, however, contrasts strongly to that found in a 1976 set of breast milk samples: 10.7 +/- 1.6 micrograms/l (n = 13) and 5.8 +/- 1.2 micrograms/l (n = 13) at 1 and 3 months post partum, respectively. The dietary selenium intake of the subjects was determined to be 33 +/- 13 micrograms/d during the course of lactation. Analytically, the results of these studies are analogous, as the same investigator determined both sets of samples by exactly the same analytical procedure.