The effect of calcium chloride (CaCl2)(5 gL-1) and sodium chloride (NaCl) concentration (40, 60 and 8 gL-1) on the microbiological and mechanical properties of naturally black olives of cv. Conservolea in brines was studied. In 40 and 60 g L-1 brines the growth of lactic acid bacteria was favoured over that of yeasts, resulting in rather complete lactic acid fermentation as indicated by high free acidity (9.8–11.5 g lactic acid L-1) and low pH (3.7–3.8). At 80 g L-1 brine, yeasts were the dominant members of the microflora, rendering a product with lower acidity (8 g lactic acid L-1) and higher pH (4.3–4.5). In the presence of CaCl2 there was a consistent increase in the depth of the peripheral region in which cell wall breakage occurred. When cells separated, perforated walls were observed at sites associated with plasmodesmata. The flesh was strongest and stiffest when CaCl2 was added to olives treated with 40 g L-1 brine, consistent with cell wall breakage being the predominant mode of failure. The only observed effect on the mechanical properties of the skin was a stiffening at 60 g L-1 brine on addition of CaCl2.