"A comparative study of the sialidase activity was performed by means of thiobarbituric acid assay and high performance liquid chromatography, using the JHA-treated larval haemolymph of Bombyx mori. The result showed that the sialidase activity increased at the larval maturation but decreased remarkably on spinning day. Accordingly, it was emphasized that the lectin activity in the haemolymph became highest after the terminal sialic acid in the sugar chains of the lectin-protein was removed with sialidase in vivo, because the content of binding sialic acid to the haemolymph protein decreased just after spinning and the lectin activity became highest just after spinning.