Neural cells isolated from the brain have a number of research and clinical applications, including transplantation to patients with neurodegenerative conditions. Tissue supply is one of the major limiting factors to clinical transplantation. Cryopreservation of primary neural cells would improve supply, aid in organisation of transplantation surgery and facilitate research. To date, cryopreservation using standard methods has resulted in reduced yield and/or viability of primary neural tissue. In order to optimise freezing protocols specifically for such cells, the non-osmotic volume (V(b)), water permeability (L(p)) and permeability to cryoprotectant (P(cpa)) were determined. Murine foetal brain tissue from the ganglionic eminence (GE), ventral mesencephalon (VM), or neocortical mantle (Ctx) was trypsinised to a single cell suspension. To determine V(b,) cell volume was measured after exposure to anisotonic solutions of sucrose (150-1500 mOsmol/kg). L(p) (mum/min.atm) and P(cpa) (mum/s) were determined for GE cells by measuring cell volume during exposure to 1.5 mol/l cryoprotectant. Cell volume was determined using an electronic particle counting method. V(b) was 27% for Ctx and GE, and 30% for VM. The osmotic response of GE cells was similar in the presence of propane-1,2-diol and dimethyl sulphoxide. In the presence of ethylene glycol, cell volume decrease was greater on initial exposure to cryoprotectant and recovery slower. Differences in L(p,) but not P(cpa), were found between cryoprotectants. The present results provide key parameters for optimisation of freezing protocols for cryopreservation of primary foetal brain tissues for application in neural cell transplantation.