It is known that cell turgor pressure affects the rigidity of plant cells and plays a major role in determining the texture of some plant tissues. The role of cell components in maintaining this turgor pressure (and therefore rigidity) during processing was studied by using agents that affect principal components of cell walls and cell membranes. Cells were prepared from carrot tissue by an enzymic method which removed the middle lamella; further treatment yielded protoplasts. Measurement of the rigidity of carrot cells and protoplasts (related to the complex dynamic modulus G*) showed that cells were more rigid and lost rigidity more slowly on heating than protoplasts. The effect of osmotic pressure on cell rigidity was examined by treating cells with mannitol solutions (0.1–1.0 M) and measuring G* at 20°C and during heating from 20 to 90°C. Cells treated with 0.1 and 0.2 M mannitol had higher initial values of G* compared with the control sample and G* increased with temperature. Cells treated with mannitol solutions above 0.4 M showed lower G* values than the control and little change in G* during heating. Carrot cells and protoplasts were treated with enzymes and the effect of the treatments on rigidity measured. Pronase (a protease) treatment of cells gave a higher initial G* value than the controls and G* also increased with temperature but lipase (EC18.104.22.168) had no effect on cells. Both Pronase and lipase had a marked effect on the rigidity of protoplasts causing a reduction in the initial G* value which decreased further on heating. Cells treated with detergents (dodecyl sulphate and Triton X-100) showed higher initial G* values compared with controls and G* increased with temperature. Microscopic studies indicated that degergents caused flocculation of the cells. With protoplasts, dodecyl sulphate caused a complete loss of rigidity and Triton X-100 also reduced the rigidity significantly. There were no signs of flocculation with protoplasts.