AbstractThe excretion of some sugars (maltose, glucose, and glucose‐6‐phosphate) was studied at pH 2.5–6.0 in 38 strains ofChlorellabelonging to 15 species of which 7 are capable and 8 incapable of symbiosis withHydra viridis. A high rate of maltose excretion below pH 4.0 (Cernichiari et al., 1969) was found only inC. vulgaris(non‐symbiotic) andC. mirabilis(non‐symbiotic). The otherChlorellaspecies are characterized by quite different patterns of sugar excretion.C. spec. (= “C. paramecii”;symbiotic) excretes very high amounts of maltose in the whole range from pH 2.5–6.0.C. kessleri(symbiotic),C. luteoviridis(symbiotic), andC. fuscavar.fusca(non‐symbiotic) show a predominant excretion of glucose‐6‐phosphate from pH 2.5–6.0. Some strains also exhibit a high excretion of glucose above pH 4.0 (C. spec. = “C. paramecii”) or below pH 3.0 (C. fuscavar.vacuolata). Several species, e.g.C. saccharophilavar.saccharophila(symbiotic),C. sorokiniana(non‐symbiotic), andC. protothecoides(symbiotic), excrete only very small amounts of sugars. There is no obvious correlation between sugar excretion and the ability or inability of theChlorellaspecies to form stabl