Data obtained from the administration of a single dose of 85 were applied to the case of daily ingestion of Sr9O. Using various intake levels of daily Sr90 ingestion, possible values for excretion, body retention, and plasma levels of Sr90 in human patients were calculated. By means of the relations found between Sr85 and Ca metabolism, the values of Sr9O for most individuals can also be obtained from urinary Ca excretion, without need for Sr85 studies. Values for body retention are in line with those found by Sr90 analysis of bone samples. A wide range of body retentions can occur in adults even on a single dietary Sr90 intake. Two methods were used to calculate Sr90 plasma levels. Both indicate that on a given Sr90 intake, plasma levels of Sr90 vary relatively little in different individuals or from children to adults. Sr90 plasma levels do vary, however, directly with Sr90 intake, and on an intake of 5 [mu][mu]c of Sr90 per day are of the order of 0.10 [mu][mu]c/liter plasma.