A review. The crucial steps of cellular photoperception are characterized and followed in real time by laser spectroscopy down to a few tens of femtoseconds. The photoactive proteins studied here are involved in major natural processes such as vision (bacteriorhodopsin used as a model of retinal chromoproteins), microorganism photomotility (photoactive yellow protein and oxyblepharismin binding protein) and plant phototropism (cryptochrome). It is also shown that the green fluorescent protein (GFP) can be used, upstream from genic therapy, as a temporal probe of cytoplasmic soly. of antibody fragments with which it is fused.