In aqueous solutions many polymers may be gelled by adding an appropriate cross-linking agent, and the system that is obtained is usually characterized by using rheological measurements. Among the most investigated properties of such systems is their gelation kinetics. In this work we deal with a system where the polymer is a nonionic polyacrylamide and the cross-linking agent is glyoxal. We focus our study in particular on the gelation kinetics by following the change in elastic modulus under given experimental conditions. In an alkaline medium and at low temperatures, the bond formation rate is found to follow certain power laws with relation to both polymer and glyoxal concentration. However, at an alkaline pH and at sufficiently high temperatures, the system loses its gelled structure due to a ’parasitic’ chemical reaction. This reaction may be eliminated by reducing the pH to an acid value, but at the same time the gelation kinetics become modified as the complexation process is then different from the alkaline case.