The perception of modal and falsetto registers was analyzed in a material consisting of a total of 80 vowel sounds sung by 10 choir singers, 40 sung in modal register and 40 in falsetto register. These vowel sounds were classified by sixteen expert listeners in a force choice test and the number of votes for modal was compared with the voice source parameters (1) Closed Quotient (Qclosed)and (2) level difference between the two lowest source spectrum partials (H1 - H2). Tones with a high value of Qclosed and low values of H1-H2 were typically associated with high number of votes for modal register, and vice versa, Qclosed showing the strongest correlation. Some singer subjects produced tones that could not be classified as either falsetto or modal register, suggesting that category perception of registers is not always feasible.