A macroion solution is modelled by an unsymmetrical mixture of macroio
ns, neutral macroparticles and counterions. The solution is analysed u
sing a symmetric Poisson-Boltzmann theory, and qualitative agreement f
ound with hypernetted chain calculations when the exclusion volume ter
m in the Poisson-Boltzmann theory is treated by the Percus-Yevick unch
arged hard sphere distribution function.