SummaryGraded doses of monomethylhydrazine (MMH) were applied to a 300-cm2 area of the shaved chest of anesthetized dogs. The area of skin to which the MMH was applied was reddened within 5 min, and the color progressively changed to deep red, then to yellow-brown to dark purple and, after 6 hr, to light gray. The area of application swelled markedly within 10-20 min. Swelling persisted for 3 hr, then gradually decreased and disappeared by 6 hr. MMH was detectable in the blood within 30 sec after the initial application. With doses less than 3 mmoles/kg, blood MMH levels rose to a peak in approximately 1 hr, and decreased slowly during the next 5 hr. As size of dose increased, higher peak levels of blood MMH were reached and the rate of subsequent decline decreased until, with doses of 4-6 mmoles/kg, no decline was seen during the 6-hr period of observation. Within 3-5 min after application of large doses of MMH to the skin, methemoglobinemia was observed. Levels of methemoglobin rose to a peak at about 2...