Intermittent bolus administration of calcitriol – i.e., 1,25-dihydroxycholecalcife-rol or 1,25-(OH)2D3 20 pmol/l, normal 1-6 pmol/l) levels were randomly allocated to daily administration of 0.75 μg calcitriol (continuous) or twice weekly administration (intermittent); the two protocols provided an identical total weekly doses of 5.25 μg calcitriol. Patients were dialyzed with a dialysate Ca concentration of 1.75 mmol/l and had oral CaCO3 or Ca acetate. 1,84-iPTH (immunoradiometric assay) and serum Ca and Pi levels were measured weekly. At the beginning of the study, the median 1,84-iPTH value was 37 pmol/l (range 20-115) in the intermittent versus 36 pmol/l (range 21-72) in the continuous calcitriol group. After 2 weeks, the median 1,84-iPTH level was 18.5 pmol/l (range 1.4-106) versus 18 pmol/l (range 1.2-48). After 12 weeks, 11 of 21 of the patients in the intermittent and 18 of 24 patients in the continuous group had reached the treatment goal, i.e., 1,84-iPTH 2.2 mm