Both lipase from runner beans and a protease (pronase) initially cause increased intensity dependence of the DCPIP Hill reaction of spinach chloroplasts. This is followed by an increase in the extrapolated zero intensity quantum requirement. Pronase treatment of the chloroplasts causes rapid changes in absorption and ORD spectra, whereas the effect of lipase treatment is much less pronounced. Long treatments of the thylakoids with the lipase and protease cause unique morphological changes within the membrane. These changes are used to assign chemical compositions to some of the structures revealed by freeze-etching.