[en] A theoretical study was made of the effect of ion streaming on the wave length profiles and total intensities of optically thick lines emerging normal to the axis of an axisymmetric expanding plasma, such as a laser-produced plasma. The ion streaming velocity (in combination with other parameters) is treated as a variable and the results from the limit where ion streaming is negligible (and so are of interest to most laboratory plasmas) to the limit where ion streaming is the dominant cause of line broadening. The effect of ion streaming is to reduce the depth over which photons can interact with plasma ions and consequently to reduce the plasma opacity. Of particular is the fact that a source function with a central maximum can couple with ion streaming to produce a self-reversed line whose red peak is enhanced and blue peak suppressed, and that resonance line profiles of this shape have previously been observed in laser-produced plasmas. (author)