A group of lipoproteins with molecular sizes of approximately 30 kDa, referredto as 30K proteins, are synthesized in fat body cells in the fifth instar larvae of silkworm,Bombyx mori. Analyzing the silkworm genome and its expressed sequence tags (ESTs), wefound 10 genes encoding 30K proteins, which are mainly distributed in three subfamilies.Of these, seven coding proteins were found to harbor the degrading sites of 30kP proteaseA, although the number of degrading sites may be different. As some potential corepromoters and regulatory elements were supposed to be essential for gene transcription, theexpression profiles of these genes were examined by semi-quantitative reverse transcriptionpolymerase chain reaction. Eight 30K protein genes were detected to express luxuriantly inthe fat body, while two were hardly expressed. Such results suggest that these 30K proteinsmay have different functions, and their adjacent regulatory elements play a crucial role inregulating their transcription.