An exhaustive search of the Ginga data on &ggr;‐ray burst GB870303 reveals two separate time intervals during which statistically significant line features are evident. One (previously unreported) interval shows a single prominent line feature at ≊20 keV; a second, corresponding to the interval reported by Murakamietal., shows two line features at ≊20 and 40 keV. From model fits to the data, we find that both sets of lines are well‐described by cyclotron resonant scattering in a magnetic fieldB≊1.8×1012G, and that the differences in the line strengths between the two intervals are significant. The variations are qualitatively similar to those produced by a change in the viewing angle &thgr; relative the magnetic field. We conjecture that the change in &thgr; is due to rotation of the neutron star, and derive limits 45 sec ≲P≲180 sec on the rotation periodP.