Recently, 99mTc-hydroxymethane dephosphonate (HMDP) has been proposed as a bone-seeking agent. A prospective clinical crossover study was undertaken in volunteers and patients for a quantitative and qualitative comparison of HMDP and MDP (99mTc-methylenediphosphonate). Results indicate that there is no appreciable difference between HMDP and MDP as bone-scanning agents within 5 h of i.v. administration.