The investigation of the dilute range in the system of myristic acid, cetyltrimethylammonium hydroxide, and water shows that the formation of charged catanionic microcrystallites induces measurable osmotic pressures. In the coexistence region between the lamellar phase and the disk phase, we observe a slight osmotic pressure drop, which is due to the crossing of tie lines during dilution. With the application of the Poisson-Boltzmann theory, the surface charge densities of icosahedral and disklike particles are estimated to determine the equation of state of these self-assembled aggregates in the dilute regime. In typical conditions, a hollow crystallite of 1-mum diameter has an effective charge on the order of 1.8 x 10(6), while the structural charge is 1 order of magnitude larger.