[The effect of the time of methotrexate administration over 24 hours on the antitumor activity of the preparation, its concentration in the blood and in the tumor in Pliss' lymphosarcoma in rats].

A mismatch between a circadian rhythm of blood-methotrexate level and that of the drug concentration in rat transplanted lymphosarcoma tissue was established. The drug proved 3 times more effective when given at the time of the day when its concentration in tumor tissue was likely to be the highest.