Nanoparticles intended for use in the transmucosal delivery of macromolecules were prepared by the ionic gelation of chitosan (CS) hydrochloride with pentasodium tripolyphosphate (TPP) and concomitant complexation with sodium alginate (ALG). The incorporation of a small proportion of ALG of increasing molecular weight (M-w; from 4 to 74 kDa) into the nanoparticles led to a monotonic increase in colloidal size from similar to 260 to similar to 525 nm. This increase in size was regarded as a consequence of the formation of gradually more expanded structures. Insulin, taken as a model peptide, was associated to CS-TPP-ALG nanoparticles with efficiencies in the range of similar to 41 to similar to 52%, irrespective of the M-w of the ALG incorporated in the formulation. These CS-TPP-ALG nanoparticles exhibited a capacity to enhance the systernic absorption of insulin after nasal administration to conscious rabbits. Interestingly, it was observed that the duration of the hypoglycaemic response was affected by the ALG's M-w. Briefly, this work describes a new nanoparticulate composition of potential value for increasing nasal insulin absorption.