As part of a program to study the chemical composition of algal biomasses, the composition of the unsaponifiable matter of the lipids of ten algal species (fiveMyxophyceae and fiveChlorophyceae) was investigated. The total unsaponifiable content, its general composition, and the components of the hydrocarbon fraction are discussed in the present paper. The unsaponifiable content of green algae is constantly higher than that of the blue‐green ones, with the exception ofChlorella. In both algal classes, the major components are hydrocarbons and sterols. Blue‐green algae are richer in hydrocarbons, whereas the green ones contain higher amounts of sterols. In most of the species examined, at least 48 components are present in the hydrocarbon fraction. Each algal species shows a characteristic gas liquid chromatography pattern, but n‐C17 is always one of the most abundant components. Generally, the prokaryotic blue‐green algae show a simpler hydrocarbon composition than the eucaryotic green algae, which contain higher amounts of high mol wt components. Unsaturated hydrocarbons are generally present in very limited quantities, with the exception ofSpirulina sp. andChlorella, sp., which contain a C17 alkene. Green algae also contain appreciable amounts of a C27 monoene and of squalene.

The composition of the terpenic alcohol and sterol fractions of the unsaponifiables of ten algal species, fiveMyxophyceae and fiveChlorophyceae, is discussed. The major component of the terpenic fraction is phytol, a diterpenic alcohol. Minor amounts of straight chain and triterpenic alcohols are also present. Practically all the species examined contain ten components in the sterol fraction: cholesterol, brassicasterol, Δ5‐ergostenol, poriferasterol, Δ7‐ergostenol, clionasterol, chondrillasterol, Δ5‐avenasterol, Δ7‐chondrillastenol, and an unidentified component. Identification of the sterols was made by gas chromatography‐mass spectrometry, and a 24 S configuration was assumed. The prokaryotic blue‐green algae are characterized by a higher content in cholesterol (3.5–14%) than the eucaryotic green algae (0–2.5). Also, brassicasterol, poriferasterol, clionasterol, and Δ5‐avenasterol are more abundant in blue‐green algae. Δ7‐Ergostenol, chondrillasterol, and Δ7‐chondrillastenol predominate, on the contrary, in green algae.

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