The relationship between calcium absorption and gastric emptying and the precision of measurement of fractional calcium absorption using a single isotope technique were evaluated in 14 normal postmenopausal women (age range 61-72 years). On two occasions separated by between 5 and 15 days, each subject was given 250 mL water containing 0.2 MBq of 45Ca in 20 mg of calcium carrier as the chloride, 20 mg kg-1 paracetamol and 9 MBq of 99mTc sulphur colloid. Venous blood samples were taken at -2, 15, 30, 45, 60, 90, 120, 150 and 180 min after consumption of the drink, and gastric emptying (GE) was monitored with a gamma camera. Fractional calcium absorption in the first hour (alpha 6) was calculated from the blood samples obtained at 15, 30, 45, 60, 90 and 120 min. An absorption rate was also derived from the 60 min sample using only a calibration curve (alpha 1). There were close correlations between radiocalcium absorption on the two study days (r = 0.89, P < 0.001 for both alpha 1 and alpha 6) and between alpha 1 and alpha 6 (r = 0.93, P < 0.001). Plasma paracetamol concentrations at 15 min were directly related to the early phase of GE (r = 0.42, P < 0.05). In contrast, calcium absorption was inversely related to GE (r = 0.45, P < 0.05). We conclude that radiocalcium absorption is not greatly influenced by gastric emptying rate and that the single blood sample procedure has similar precision to the six-blood sample test.