The use of drawing as an assessment tool to reveal students' conceptions in biology specifically on human organs and organ systems is not new, however, there is a deficit in the literature that attempted to explore and reflect on its usefulness and relevance specifically, in eliciting students' preconceptions related thereto. Making use of a convergent mixed methods design, this paper presents the first phase of a sequential study on the development and implementation of a teaching sequence on human organ systems, that is the use of drawing in aggregating preconceptions on human organs and organ systems from among 138 pre-service teachers. The drawings underwent content and thematic analysis informed by the level of the biological quality of drawings. Results showed that a great majority of the participants possess limited and inconsistent conceptions that needed to be addressed systematically. Taking into consideration the purpose of eliciting and nature of students' preconceptions, as well as the inherent strengths and limitations of drawing as a tool for assessment, a reflection on the relevance of drawing as a tool in eliciting students' preconceptions is provided.