This study investigated the hypothesis that breathiness used contrastively or to enhance a contrast in a language is as ‘‘breathy’’ as breathiness resulting from vocal pathology. Vowel samples were taken from four male and four female native speakers of English and four male and four female speakers with pathologically breathy voices. In the English data, a single pitch period was extracted and analyzed from an allophonically modal sample (following /ʔ/), a vowel-initial allophonically breathy sample (following /h/), and a vowel-medial allophonically breathy sample. A representative vowel-medial cycle was selected for speakers with vocal pathology. To determine relative breathiness, vowels were inverse filtered and fit with the LF model of the glottal flow derivative; measurements of open quotient, glottal skew, excitation strength (Ee) and the shape of the return phase were made from the LF smoothed pulses. Breathiness occurring allophonically after intervocalic /h/ did not differ significantly on any parameter from the vowels produced by speakers with pathologically breathy voices. EE proved to be the best measure of relative breathiness. It distinguished the pathological samples from the normal samples (allophonically modal and allophonically breathy together); it also distinguished the allophonically breathy samples from the allophonically modal samples.