[Compliance, concordance, adherence].

Ambulatory pharmacotherapy is marked by many deviations, mostly downward, in drug dosing from prescribed instructions. Soundly compiled dosing histories date from 1977, based on electronic time-stamping of medication 'events': package entry times, done first with eyedrop dispensers for glaucoma drugs. Electronically monitored packages for oral dosage forms date from 1988. Since then, expanding data have brought many surprises, as evidence has replaced eminence in clinical views regarding discrepancies between prescription and reality. Key features of electronic monitoring are: automaticity of time-stamping, inviolable data, and high rates of data-sampling (60/hr vs 2 - 12/yr with older methods), revealing time-of-day, day-of-week, and white coat effects that facilitate medication management, opening new ways to improve care.