For the purpose of determining the shelf life of 1% Methylene Blue (MB) injection, its stability was investigated under 4 storage conditions for 30 weeks. The content of MB in 1% MB injection started to decrease at 5°C in the dark 4 weeks after preparation, but no significant differences were observed under three other storage conditions (at room temperature (22.0±0.5°C) and at 40°C in the dark and at room temperature (22.0±0.5°C) in 1000 Lux fluorescent light) for 30 weeks. According to these results, we changed the shelf life of 1% MB injection from 2 to 6 months and the frequency of preparation from six times to twice/year. The unit cost before and after the change of shelf life was compared. One unit cost calculated according to materials costs and labor costs was ¥2, 738.6 during the 1993-1995 period (six times preparations/year), while it was ¥1, 545.9 during the 1996-1998 period (twice preparations/year). A cost savings of ¥1, 192.7/ampule (43.6%) was produced by changing the frequency of preparation from six times to twice/year. In addition, the discard cost for 1% MB injection past its shelf life was estimated. A discard cost saving of ¥85, 766.8/year (75.2%) was achieved by changing the frequency of preparation from six times to twice/year. Furthermore, the working hours were reduced by 9.58 hours/man/year and it allowed pharmacists to utilize the extra time gained by changing the frequency to other work.