3-Phosphoglycerate- and oxaloacetate-dependent O2 photoevolution by permeabilized cell preparations (Pressates), prepared from wild type (Wt) and two reductive pentose phosphate cycle mutants of Chlamydomonas reinhardtii showed different sensitivities to the inhibitors sodium cyanide and sodium azide. NaCN (1.5 millimolar) severely inhibits both CO2- and 3-phosphoglycerate-dependent O2 photoevolution by the Wt Pressate, but does not inhibit 3-phosphoglycerate-dependent O2 photoevolution by Pressates prepared from the mutants rcl-u-1-10-6C (which lacks ribulose, 1-5, bisphosphate carboxylase activity) and F60 (which lacks phosphoribulokinase activity). NaN3 (0.5 millimolar) inhibits 3-phosphoglycerate-dependent O2 photoevolution by the rcl-u-1-10-6C Pressate more severely than in the Pressates prepared from F60 and Wt. A higher concentration of NaN3 (2.0 millimolar) severely inhibited oxaloacetate-dependent O2 photoevolution by the rcl-u-1-10-6C, but not by the F60 Pressate. O2 exchange-dependent upon methyl viologen was not strongly inhibited by 2 millimolar NaN3 in either of the mutant Pressates. The data suggests that the mutational lesions which resulted in decreased ribulose-1,5-bisphosphate carboxylase and phosphoribulokinase activities effected changes in other photosynthetic reactions, either by direct interactions between component proteins or by causing changes in substrate or cofactor availability to the partial reactions.