This paper reports the results and the interpretation of rheological experiments on and diffusion measurements of fluorescent polymer chains in solutions and gels of dextran (dex) derivatized with methacrylate (ma) groups. We illustrate the use of confocal scanning laser microscopy (CSLM) and fluorescence recovery after photobleaching (FRAP) to study the mobility of large molecules in polymer systems. The main aim was to understand the influence of the polymer network in the gels on the mobility of large molecules. Therefore we measured the diffusion coefficients before and after cross-linking the dextran methacrylate (dex-ma) chains. Increasing the dex-ma concentration did not spectacularly increase the sterical hindrance by the dex-ma network. However, the sterical hindrance did become significantly stronger when the size of the diffusing probe and the degree of ma substitution were increased. The mobility of the probes decreased when the dex-ma gels became more elastic. However, the decrease in the diffusion coefficient was much less than the spectacular increase in the elasticity of the hydrogels.