Electronic Journal of Differential Equations, Vol. 2007(2007), No. 109, pp. 1-11. Title: Initial-boundary value problems for nonlinear pseudoparabolic equations in a critical case Author: Elena I. Kaikina (Univ. Nacional Autonoma de Mexico, Morelia, Mexico) Abstract: We study nonlinear pseudoparabolic equations, on the half-line in a critical case, $\displaylines{ \partial _{t}( u-u_{xx}) -\alpha u_{xx}=\lambda |u| u,\quad x\in \mathbb{R}^{+},\; t>0, \cr u( 0,x) =u_{0}( x) , \quad x\in \mathbb{R}^{+}, \cr u(t,0)=0, }$$ where $\alpha >0$, $\lambda \in \mathbb{R}$. The aim of this paper is to prove the existence of global solutions to the initial-boundary value problem and to find the main term of the asymptotic representation of solutions. Submitted March 22, 2007. Published August 7, 2007. Math Subject Classifications: 35Q35 Key Words: Dissipative nonlinear evolution equation; Sobolev equation; large time asymptotic behavior.