Intranasal (i.n.) neostigmine has been developed to obtain a quicker onset of action and a more adaptable dosage regimen than oral neostigmine. The effect of this neostigmine formulation in myasthenia gravis (MG) was studied by means of computer analysis of saccadic eye movements (SEMs). Six MG patients were selected on the basis of a positive effect of Tensilon on hypometria of the first saccade. The effect of the i.v. formulation (0.5 mg) was compared to 1, 2, 3, and 4 puffs of i.n. neostigmine (one puff = 4.6 mg). The drug effect on SEMs was monitored at intervals up to 2 h. Administration of i.v. neostigmine produced a marked effect immediately after the injection and the benefit lasted over 1 h. Following administration of i.n. neostigmine a marked effect was found for two, three, and four puffs. The drug effect was evident within 3 min, peaked at 18-33 min, and lasted over 2 h. Our data indicate the efficacy of the new formulation of neostigmine in MG as measured by means of quantitative analysis of SEMs.