The step filter has previously been shown to be useful in assessing equivocal lesions in brain scinitigraphy. The filter is very simple, requires al most two minutes computing lime and, when the collimator characteristics are specified, is independent of the operator. It gives the clinician a number based on count statistics which he can relate to the equivocal area in question. The problem of interpretation is discussed and examples of normal, abnormal and equivocal brain scintigrams are displayed before and after filtering. Cases which require a certain amount of caution are also discussed.