  Using the one-parameter internal symmetry group in the Bianchi type-I
spacetime for cosmological models with a perfect fluid, we show that a system
of coordinates exists in the associated internal space where two scale factors
become equal. We find the general solution for an anisotropic model containing
a perfect fluid with constant baryotropic index and investigate the asymptotic
regimes. We obtain exact solutions for a set of anisotropic fluids which
includes an anisotropic stiff fluid.
