  We consider a system of nonlinear spinor and a Bianchi type I gravitational
fields in presence of viscous fluid. The nonlinear term in the spinor field
Lagrangian is chosen to be $\lambda F$, with $\lambda$ being a self-coupling
constant and $F$ being a function of the invariants $I$ an $J$ constructed from
bilinear spinor forms $S$ and $P$. Self-consistent solutions to the spinor and
BI gravitational field equations are obtained in terms of $\tau$, where $\tau$
is the volume scale of BI universe. System of equations for $\tau$ and $\ve$,
where $\ve$ is the energy of the viscous fluid, is deduced. This system is
solved numerically for some special cases.
