Aggravation of human and experimental myasthenia gravis by contrast media. After observing a 72-year-old myasthenic patient develop an acute myasthenic exacerbation following the administration of routine diagnostic IV contrast material, an observation rarely described in the literature, we used the experimental autoimmune myasthenia gravis model in rabbits injected with a contrast agent to simulate the situation. There was significant worsening of the decremental response to 3 Hz repetitive nerve stimulation from 40 +/- 29% to 55 +/- 27% following the IV administration of contrast agent at doses similar to those used in humans. IV calcium partially reversed this aggravation. Caution is merited when myasthenic patients are administered contrast media. 