Towards the development of a drug delivery vehicle for the nasal delivery of insulin, N-trimethyl chitosan has been co-formulated with poly(ethylene glycol) and glycerophosphate into a thermosensitive hydrogel structure, the sol-to-gel transition properties of which occur at physiologically relevant temperatures over optimally brief timescales. In vitro experiments mimicking those of the nasal environment have indicated the dual capability of the formulation to affect the opening of tight junctions and to release its therapeutic content in a controlled manner, while spectroscopic and analytical investigations have indicated the structural integrity of the incorporated insulin. The in vivo potential of this in situ thermogelling nasal formulation to act as a once-a-day dosage form for the intranasal delivery of insulin has been demonstrated in the diabetic rat model.