Most naturally occurring musk fragrances are macrocyclic lactones and ketones with a ring size between C14 and C18.1 These natural products, isolated from both plant and animal sources, are used in expensive perfumes, while synthetic musks, often of very different structures, are used to supply the bulk of the musk fragrance market. The first musk to be chemically characterised was ambrettolide (16-hexadec-7-cis-enolide), which occurs in ambrette (Hibiscus abelmoschus) seeds.2 Further C10-C14 fragrance compounds, including 14-tetradec-5-cis-enolide and alkyl acetates, were later identified in distillates from ambrette seed extracts by Maurer and Grieder.3 With the purpose of investigating the biosynthesis of the macrocylic lactone musks, we recently conducted an analysis of the fragrance compounds in ambrette seeds.4 These are all monoesters, and are comprised of decyl (3%), dodecyl (3%) and tetradec-5-enyl (0.5%) acetates; 14 tetradec-5-enolide (0.5%), 16-hexadec-7-enolide (11%) and 18-octadec-9-enolide (7%); and 2-cis, 6-trans-(3%) and 2-trans, 6-trans-farnesyl acetate (72%). The numbers in parenthesis give a typical composition within the monoester fraction. The fragrance monoesters are present in the seed coat, at 0.3% of the dry weight of the whole seed. They are deposited during the period of embryo maturation (20-35 days after flowering) and not during the prior period of seed coat formation (5-20 days after flowering). This communication describes our first in vivo labeling experiments with developing ambrette seeds.