This study compares the six commercially available kits for preparing methylene diphosphonate. The kits were randomly assigned to 134 bone examinations such that neither the physicians nor the technologists knew which brand of tracer was used. Thigh activity quantitatively varied significantly among the kits (P = 0.019). Detectable gastric activity also varied by brand. Other qualitative and quantitative measures of bone and soft tissue uptake showed no significant differences among the kits but consistently favored the Squibb product.