The most sensitive indicators of mass-loss for stars in the upper left part of the HR diagram are the UV P Cygni profiles observed in the resonance lines of common ions such as N V, Si IV, and C IV. We present here some results from a study of these lines in the high resolution IUE spectra of 197 Ï stars. Profile fits were carried out in the manner described by Prinja & Howarth (1986) for all unsaturated P Cygni resonance doublets. The parameterisations adopted enable the product of mass-loss rate (Ṁ) and ion fraction (qi) to be determined at a given velocity, such that Ṁ qi°C Ni R* v∞ , where Ni is the column density of the observed ion i, v∞ is the terminal velocity, and R⋆ is the stellar radius. The accompanying figures illustrate the behaviour of Ṁ qi (evaluated at 0.5 v∞ ) for N V and C IV.