It has been shown that, when captured in charged film microcapsules prepared from spermine alginate, intact viruses retain infectivity, isolated viral proteins retain immunogenicity, and trypsin retains enzymatic activity. However, it was unclear whether the greater anionic strength of hemisulfate residues such as those in carrageenan might alter protein conformation and activity unfavourably in comparison with the lesser influence of alginate carboxylates. Further, the influence of the structure of the amine used to prepare the capsules was largely unknown. To examine these questions, trypsin, used as a model protein, was; encased in microcapsules prepared from iota-carrageenan and oligoamines drawn from either the homologous series spermine, spermidine, putrescine or ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine. The gross structures of encapsulated and native trypsin were compared by denaturing electrophoresis and their enzymatic activity by the method of Hummel. In all encapsulations SDS PAGE gave no evidence of alteration of protein structure. When encapsulated, the apparent activity of trypsin was reduced by about 60 to 75%, but when the capsules were lysed in hypertonic saline activity was restored. This apparent reduction in activity is attributed to the diffusional barrier imposed by the encapsulating membrane but it should be recognized that it may be the result of reversible denaturation.