The guideline for industry S3A Toxicokinetics: The Assessment of Systemic Exposure in Toxicity Studies (S3A guidance) has been successfully implemented since 1994, and in recent years, analytical method sensitivity has improved, allowing microsampling techniques to be used in toxicokinetic (TK) assessment. This question-and-answer (Q&A) document focuses on points to consider before incorporating the microsampling method in TK studies, acknowledges the benefits (and some limitations) of using microsampling to assess toxicokinetics in main study animals, and acknowledges the overall important contribution of microsampling to the 3Rs benefits (replacement, reduction and refinement) by reducing or eliminating the need for TK satellite animals.