The detection of nanobubbles on surfaces is well established (e.g., AFM and optical microscopy methods), but currently no methods exist for the direct detection of bulk nanobubbles. Here, cryo-electron microscopy (cryo-EM) has been employed to observe bubbles in aqueous solutions for the first time. Nitrogen bubbles generated by a chemical reaction were observed in amorphous ice trapped between two carbon films. The cryo-EM images of bubbles showed the same features as predicted by theory. The fact that no bubbles were observed near an air-water interface suggests that bubbles may diffuse to the nearby air-water interface and escape. The estimate of the bubble diffusion coefficient is about 30-250 mu m(2)/s.