Computer algebra solving of first order ODEs using symmetry methods. A Maple V R.3/4 computer algebra package, ODEtools, for the analytical solving of first-order ordinary differential equations (ODEs) using Lie group symmetry methods is presented. The set of commands includes a first-order ODE solver and routines for, among other things: the explicit determination of the coefficients of the infinitesimal symmetry generator; the construction of the most general invariant first-order ODE under given symmetries; the determination of the canonical coordinates of the underlying invariant group; and the testing of the returned results.