Objective: 3,4-diaminopyridine (3,4-DAP) is commonly used for treating neuromuscular diseases, such as the Lambert-Eaton myasthenic syndrome, but the pharmacokinetics of 3,4-DAP base have not been investigated. We therefore studied 3,4-DAP base pharmacokinetics in healthy Japanese volunteers. Materials and methods: In this crossover study, we administered a single oral dose of 10 or 20 mg 3,4-DAP base to healthy Japanese volunteers (n = 5) after food intake, or 10 mg 3,4-DAP to fasting individuals. We measured serum 3,4-DAP concentrations, performed electrocardiography (ECG), and administered questionnaires. Results: After administration of 10 or 20 mg 3,4-DAP following food intake, the maximum serum concentrations (C-max) were 8.09 +/- 4.47 ng/mL and 35.8 +/- 15.7 ng/mL, respectively (mean +/- standard deviation; SD), and the areas under the serum concentration-time curve (extrapolated to infinity) were 639 +/- 213 ngxmin/mL and 2,097 +/- 936 ngxmin/mL (mean +/- SD), respectively. Administration to fasted individuals indicated that food intake did not significantly alter 3,4-DAP pharmacokinetics. ECG showed no clinically significant changes, but PR intervals were prolonged in all cases. Two out of 5 subjects showed perioral paresthesia symptoms after administration of 20 mg 3,4-DAP. Conclusion: This study indicated that 3,4-DAP base pharmacokinetics were non-linear. Although no clinically significant changes in ECG were observed, it is advisable to perform ECG periodically during 3,4-DAP administration in order to monitor cardiac function. Moreover, the development of perioral paresthesia may be dependent on the dose of 3,4-DAP used.