Background Pegaspargase (PEG), can cause anti-asparaginase (ASP) antibody formation, which can decrease its effectiveness without causing any clinically-apparent reaction (CAR) (silent inactivation [SI]). When a patient has SI, a switch to Erwinia ASP is warranted, but there is currently a global shortage of Erwinia. Up to 30% of patients receiving PEG will experience a CAR, while only 8% of patients will experience SI; the only way to distinguish between these is by measuring an ASP level. However, routine ASP monitoring is not currently standard of care at all Canadian centres. This study aims to identify variations in practice regarding ASP monitoring and Erwinia use. Procedure A 21-item survey was developed using OPINIO software and distributed to all Pediatric Hematology-Oncologists in Canada from Feb-Oct 2020. Results Respondents represented 15 hospitals across each region of Canada (response rate=52%). Only 39.2% of respondents reported routinely measuring ASP levels, yet 53% of respondents have modified therapy from PEG to Erwinia in up to half of their patients. The most common reason for not measuring ASP levels was not knowing how to use levels clinically (25.5%). There was variation in the timing of levels and their target. Conclusions We identified substantial variation in ASP activity monitoring practices across Canada. Therefore, future research should aim to develop a national practice guideline on ASP activity monitoring.