Content, according to Bolzano, is intransparent: our knowledge of certain essential features of the contents of our contentful mental acts is often severely limited. In this paper, I identify various intransparency theses Bolzano is committed to and present and evaluate the defence he offers for his view. I argue that while his intransparency theses may be correct, his defence is unsuccessful. Moreover, I argue that improving on his defence would require substantially modifying his general epistemology of content.