A nonstationary Poiseuille solution describing the flow of a viscous incompressible fluid in an infinite cylinder is defined as a solution to an inverse problem for the heat equation. The behavior as t → ∞ of the nonstationary Poiseuille solution corresponding to the prescribed flux F (t) of the velocity field is studied. In particular, it is proved that if the flux F (t) tends exponentially to a constant flux F * then the nonstationary Poiseuille solution tends exponentially as t → ∞ to the stationary Poiseuille solution having the flux F * .The first step in the study of the asymptotic behavior of solutions to the nonstationary Navier-Stokesin a domain Ω ⊂ R n , n = 2, 3, with cylindrical outlets to infinity is to find a Poiseuille type exact solution in an infinite cylinder Π = {x ∈ R n : x = (x 1 , . . . , x n−1 ) ∈ ω, x n ∈ R} with ω a bounded domain in R n−1 . Consider (1.1) in Π × (0, T ) and additionally prescribe the flux of the velocity field through the section ω:(1.2) Moreover, suppose that a = (0, 0, a), a = a(x ), is independent of the variable x 3 and the following necessary compatibility condition is satisfied:The nonstationary Poiseuille solution has the formwhere p 0 (t) is an arbitrary function of t and the pair (v(x , t), q(t)) is a solution to the following inverse problem(1.5) (∆ is the Laplace operator in x ). In (1.5) the functions a(x ) and F (t) are given, while v(x , t) and q(t) should be determined.Vilnius.