Individual, dormant spores of Bacillus sphaericus were studied with laser diffractometry. Correlation coefficients were obtained for the water content and radius of the protoplast and the water content and thickness of the integument of the spores. The coefficients showed that the states of the protoplast and the integument were interrelated. The water contents of the protoplast and the integument were positively correlated (rho = 0.73), and spores with thinner integuments had more dehydrated protoplasts. The coefficients were compared with qualitative predictions based on current models of the mechanism responsible for protoplast dehydration. The results did not support models involving an expansion of the cortex as the cause of the dehydration, but were consistent with cortex contraction and the model in which the cortex maintained rather than produced the dehydrated state of the protoplast.