During a vitellogenic cycle in the ovoviviparous cockroach Eublaberus posticus, more than 100 mg of lipid is transported from the fat body to the developing oöcytes. Lipid is very likely transported in the form of diglyceride (DGL), because 1- 14C-glycerol injected into the haemocoel is preferentially incorporated by the fat body into DGL, and labelled DGL rapidly appears in the oöcytes as well. Two main lines of evidence suggest that lipid transport is under the control of juvenile (gonadotropic) hormone: (1) DGL accumulates in unusual quantities in both ovaries and fat body following allatectomy, although vitellogenesis is superficially brought to a halt within one day of surgery, (2) fat body dissected from allatectomized cockroaches synthesizes only 25% as much 14C-DGL from labelled precursors as does tissue from controls.