Capillary microsampling (CMS) has recently been introduced as a response to the demands for more ethical use of laboratory animals according to the 3R principles. In CMS, an exact volume of the blood, plasma or other biofluid is collected in a capillary from which it is washed out, resulting in a diluted sample that can be handled using the existing equipment in the bioanalytical laboratory. CMS differs from traditional large volume sampling as the microsample is diluted before further handling and analysis, and reanalysis is performed using the diluted sample. This has some implications for the validation and this report is an attempt to clarify how to validate and use CMS methods in a regulatory environment. CMS also shows some distinct new opportunities: labile analytes can be immediately stabilized at sample collection and the addition of the internal standard to the whole sample can improve analytical performance. The experiences from 5 years use of CMS of plasma and blood for determination of drug exposure in animal studies are reviewed.