Aim:To evaluate the pharmacokinetics (PK) and pharmaeodynamics of the LFA3Ig fusion protein (LFA3IgFP) in healthy volunteers and patients with chronic plaque psoriasis. Methods: The clinical trials included 2 phase Ⅰ open studies. Study 1 was an open-label dose escalation study in 24 healthy vol-unteers, and study 2 was a single-group, open-label study in 12 patients with chronic plaque psoriasis. The serum drug concentrations were measured, and the concentration-time data were analyzed by compartmental analysis using the Practical Pharmacokinetic Program. Results: In study 1, after intramuscu-lar (im) administration at a dosage of 5, 15, and 25 mg, the concentration-time curves of LFA3IgFP fitted well to a 1 compartment open model. Areas under the concentration-time curves increased linearly with dose. Clearance rates (Cls/ F) and elimination half-lives (T1/2ke) had no significant difference between dif-ferent dose groups. A transient, slight decline of CD4+ and CD8+ T-cell subsets was observed after administration. In study 2, after im administration at a dos-age of 15 mg weekly for 8 weeks, the concentration-time curve was best fitted to a 1 compartment open model, with a T1/2ke, of 307.9±32.7 h. The steady state was attained after the fifth administration. Conclusion: The PK behaviors of LFA3IgFP in healthy volunteers and patients with chronic plaque psoriasis com-plied with linear kinetics within the examined dose range. A significant accumu-lation was observed after repeated administration at a dose of 15 mg weekly for 8 weeks.