To determine the IOP lowering effect of latanoprost 0.005% when added to patients already on maximum tolerated medical therapy and not at target IOP. Design: Eye Clinic records of glaucoma patients at the Baltimore VAMC who were on maximum tolerated medical therapy and who had latanoprost 0.005% added to their drug regimen due to unacceptably high IOP levels were reviewed. The 18 patients whose findings were analyzed for this study were all male veterans ranging in age from 53 to 82 years. The mean age was 73.3 years. All but one of the subjects were African-American. Three baseline IOP readings were taken before patients were started on latanoprost. Patients were then followed at their regular appointments and the resultant change in intraocular pressure was assessed. Statistical significance was determined by Student's t-test and by defining the correlation coefficient. Results: The addition of latanoprost 0.005% additionally lowered IOP by an average of 21% for patients already on maximum tolerated medical therapy. This effect was statistically significant at P < 0.01. Seventy-two percent of the subjects reached their target IOPs. There was a trend toward higher IOP reduction with higher baseline IOP, but no direct correlation was found. There was a general decrease in the percentage of subjects reaching target pressures as the number of medications taken increased. Of those patients not on pilocarpine, a greater number reached their target pressures. The difference in the amount of patients reaching their target pressures on and off pilocarpine was mildly significant at P < 0.5. However, the difference in percentage drop in IOP between these two groups was not significant. Conclu.rion: This study indicated that latanoprost 0.005% was useful in lowering IOP in patients already on maximum tolerated medical therapy. A large percentage of patients taking pilocarpine as part of their drug regimen had a therapeutic lowering of IOP when latanoprost was added. This indicates there may be an additivity of latanoprost to pilocarpine when they are used together in clinical practice. 0 1997 Elsevier Science Ireland Ltd.