A computer program “MULTCOMP*” was developed to provide a prescription for the preparation of multicomponent electrolyte solutions which allow the study of plant response to osmotic stress and/or specific ion toxicity. The solutions may comprise five components (Ca, Mg, Na, Cl, and SO4) of any desired Ca:Mg and Cl:SO4 stoichiometric ratio and sodium adsorption ratio (SAR). The program also carries out chemical speciation of the prescribed solutions, or solutions of similar composition, taking into consideration 12 chemical species (Ca2+, CaCl+, CaSO4, Mg2+, MgCl+, MgSO4, Na+, NaCl, NaSO4−, Na2SO4, Cl−, and SO42−). Consequently, the obtained activity of each chemical species may further help in understanding a plant’s response to specific ion toxicity. The program is written in FORTRAN and compiled by a FORTRAN compiler (version VAX/VMS) to allow its running on IBM or compatible personal computers.