Four different 99mTc labeled P-based bone-imaging agents were compared by a scan-evaluation technique in which the skeletal uptake was visually assessed at selected sites. A detailed statistical analysis of scans, by each of 3 independent evaluators, on a total of 140 different patients showed that 2 of the agents (based on pyro- and on trimetaphosphate) were superior. The statistical analysis showed good agreement between the investigators and consistency in their repeat evaluations.