Purpose. To investigate the activity profile of cyclic nucleotide phosphodiesterase (PDE) isoenzymes and the effects of isoen-zyme selective inhibitors in the superior and inferior lacrimal glands, Harderian gland, and zygomatic gland of the rabbit.Methods. Protein fractions extracted from crude homogenates on an anion exchange column were examined for PDE activity using an HPLC method for detecting nucleotides.Results. The superior and inferior lacrimal glands had identical PDE activity profiles. PDE 1 was the major type of activity and there was also a minor PDE III peak of activity. The main activity detected in the lipid secreting Harderian gland was PDE II and for the mucus secreting zygomatic gland PDE III. All glands contained PDE IV activity. The kinetics of the peak enzyme activities were examined and found similar, but not identical to the kinetics for PDE activities obtained from other tissues. Inhibitors of specific PDE classes and the general PDE inhibitor, IBMX, were tested on the peak enzyme activities. Activities designated by their substrate specificity or co-factor modification were most strongly inhibited by the corresponding class selective inhibitor. For example, PDE I activity in the lacrimal gland was most strongly inhibited by nicardipine. All activities were inhibited by IBMX.Conclusions. The superior and inferior lacrimal glands of the rabbit have the same PDE profile and this differs from the PDE subtypes detected in the mucus secreting zygomatic gland and the lipid secreting Harderian gland.