The effects of added iota-carrageenan (IC), guar gum (GG), locust bean gum (LBG), or dextran (Dx) on the isotropic-nematic phase equilibrium of kappa-carrageenan (KC) in solutions of 0.1 M NaI were studied. The concentrations of the polysaccharides in the separating phases were determined by NMR, and the phase volumes were observed, at different mixing ratios. All added polysaccharides were enriched in the isotropic phase, but to very different extents. GG partitioned relatively evenly between the two phases, and its effect on the relative phase volumes was very small. Dx was moderately enriched in the isotropic phase. LEG was different from the other added polysaccharides in that already relatively small amounts prevented a macroscopic phase separation, probably due to the increased viscosity. IC was exceptional in that it showed a very strong preference for the isotropic phase. As a consequence, the relative phase volumes were affected on addition of IC, and the nematic phase appeared at a much lower KC concentration than for KC alone. The reason for the exclusion of IC from the nematic phase is not clear, but it is speculated that it could depend on a tendency to form aggregates.