At fixed lung volume (V_L), alterations in surface tension change alveolar surface area (S) and lung recoil (P_L). Wilson (1982), using data from fixed lungs (Bachofen et al. (1979) and Gil et al. (1979)), quantified the isovolume change in S with P_L. We reexamined this question in fresh excised rabbit lungs with two important differences. First, we measured fractional changes in S using diffuse light scattering, avoiding the potential upset of the balance of tissue and surface forces during fixation. Second, we altered surface tension by ventilating the lungs with nebulized polydimethylsiloxane, with much less residual fluid compared with lavage. We found that S decreased at low and mid V_L (treatment surface tension > control) by about half Wilson's estimates, and was nearly unaffected by treatment at high V_L. This suggests that with increased surface tension there is (1) greater septal retraction in lungs fixed by vascular perfusion compared with unfixed lungs, and (2) a greater increase in P_L and less loss of S than would have been predicted.