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A laboratory method was developed to evaluate the sound transmission characteristics of road vehicle body seals. Primary bulb seal samples were mounted in a fixture which approximated the geometry of a typical door-gap cavity. The seal fixture was integrated with a rigid panel into the floor of a quiet, low-speed, closed test-section wind tunnel. Flow-excited pressure fluctuations in the door-gap cavity were induced by the air stream instead of by sound waves in a quiescent environment as in standard transmission loss measurements. A soundproof anechoic enclosure located underneath the test-section floor isolated the sound receiver. The sound level reduction between the cavity pressure and the sound pressure into the enclosure, a quantity directly related to the sound transmission loss (TL) in this case, was measured accurately between the 1250 and 5000 Hz one-third octave bands.