Three new sesquiterpene hydroquinones peyssonol A and B (5 and 6 and hyatellaquinone (7) have been isolated from the alga Peyssonnelia sp. and the sponge Hyatella intestinalis. The structure of the three compounds was determined mainly by NMR measurements. Peyssonol A (5) is the first reported bromo sesquiterpene hydroquinone. Several of the new compounds were found in a preliminary test to inhibit the reverse transcriptase of human immunodeficiency virus (HIV).