[en] With high-resolution laser spectroscopy plasma effects of four single hydrogen Balmer-α fine structure transitions have been investigated in a He-H dc discharge. For charged-particle densities of 10⁸ to 10¹¹ cm^-3 the signs and magnitudes of shift and broadening can be explained with linear and quadratic Stark effect by treating both electrons and ions in impact approximation and by taking inelastic fine-structure transfer collisions into account. Contributions to the understanding of plasma effects and the method for low-density plasma diagnostics are discussed. (orig.)