Abstract: The invention relates to new polyalkyl indan-1-ones, to processes for manufacturing them and to the use thereof in perfumes. The new products are polyalkyl substituted hydrindacen-1-ones and polyalkyl substituted hexahydro benz(f) inden(1H)-1-ones belonging to the family of substances defined by the following formula: ##STR1## in which R1, R2, R3, R4 are H or an alkyl radical having one to three atoms of carbon and X is a --CHR5-- group or a --CHR5--CHR6-- group in which R5 and R6 are H or CH3 and at least three of the radicals R1, R2, R3, R4, R5 and R6 are alkyl radicals.