SUMMARYAbsorption of the diphosphonate etidronaEe (HEDP) was measured in 20 volunteer subjects at two centres (Glasgow and Madison) using a new method based on simultaneous administration of HEDP and intravenous99Tc‐HEDP (Osteoscan). The mean absorption of HEDP in fasting subjects in Glasgow was 3.5% (range 1–8.9%) and in Madison 1.5% (0.7–2.8%) (P<0.035). In four subjects studies were repeated with good agreement between results (mean 3.9 cf. 3.5%). Six subjects had studies repeated when drug was ingested with food and in all cases absorption was effectively reduced to zero. We conclude that absorption of HEDP is significantly higher in normal subjects in Glasgow than in Madison. This may be of importance with regard to the finding of histological osteomalacia and fracture associated with HEDP use in Gl