Garlic (Allium sativum L.) calli in vitro were evaluated over a range of salt concentrations and by adding mannitol to culture medium with reduced salt to provide equivalent osmoticum. The water potential of the medium ranged from -0.27 to -0.73 MPa under the various salt and osmotic stress conditions. The percent increase in calli was highest in standard Murashige & Skoog (MS) medium and was reduced when MS salts were reduced but the water potential of medium was adjusted to that of standard MS medium by addition of mannitol. The water potential of callus tissue was similar to that of tissue culture media over a 20-fold range (10% to 200%) of MS concentrations. Turgor of callus tissue was not influenced by any stress conditions. These results indicate that the optimum concentration of salt and water status of medium for formation of garlic calli was provided by standard MS medium.