Abstract
SYNOPSIS. Defined media for Leptomonas collosoma, L. mirabilis, and L. sp. from Dysdercus are described. In addition to factors required by Crithidia spp., including a source of Crithidia factor, all 3 organisms require glycine. Leptomonas collosoma and L. sp. from Dysdercus require choline. All trypanosomatids thus far studied require calcium pantothenate but L. collosoma has an especially large requirement. Leptomonas mirabilis but not L. sp. from Dysdercus can synthesize methionine from homocysteine thiolactone during growth. Homocysteine thiolactone is toxic to L. sp. from Dysdercus. Methionine plus vitamin B12 partly annul homocysteine thiolactone toxicity but only if glycine is also present.