BACKGROUND: Screening for primary aldosteronism is infrequently performed in primary care. This is partly because screening is complicated by the need to adjust existing antihypertensive medications. This article provides an approach to screening patients who are already taking antihypertensive medication. OBJECTIVE: The objective of this article is to describe how to alter antihypertensive medications to allow accurate screening for primary aldosteronism. DISCUSSION: The ideal time to screen for primary aldosteronism is prior to initiating antihypertensive medications. If the patient is already undergoing treatment, replacing commonly used medications with sustained-release verapamil, prazosin, moxonidine and/or hydralazine results in fewer false positives and false negatives. Accuracy is also improved by ensuring normokalaemia. Screening should be performed six weeks after these conditions are met. A positive result should trigger a referral to an endocrine hypertension unit for further evaluation.