Swelling behavior of kappa-carrageenan gels in water and KCl solutions was investigated by photon transmission experiments following the preparation of gels in the presence and absence of externally added K+ ion as a gel promoting agent. Transmitted photon intensity, I-tr, increased continuously during swelling depending on the carrageenan and ion content in the gel. This increase in I-tr was modeled using the Li-Tanaka equation. Both the experimental work and the model showed that the swelling of low carrageenan and ion content gels took less time than that of high ion content gels. It is confirmed that double helices in a swollen gel move much faster in pure water than in KCl solution during swelling processes. Swelling time constants, tau(I), and collective diffusion coefficients, D-o, were measured for the gels swollen in water and KCl solutions. (C) 2003 Wiley Periodicals, Inc.