When glaucoma medication fails to adequately control intraocular pressure (IOP), a second medication is frequently added. Before adding a second drug to patients whose IOP was no longer controlled by 0.5% timolol, we tested the effect of switching to another beta blocker, levobunolol (0.5 or 1%). We also evaluated the effect of study participation on compliance in the control group continuing to receive 0.5% timolol. In each treatment group, the IOP of approximately 30–40% of the patients was successfully controlled for the 3-month study period. The remaining patients did not exhibit significant pressure reductions and were dropped from the study within 2 weeks. We concluded that (1) the results of’switch’ studies without a control group must be interpreted carefully, and (2) the initiation of a ‘new regimen’ with an equieffective beta blocker may be sufficient to increase compliance and thereby control IOP.