Hairy root systems have proven to be a viable alternative for recombinant protein production. For recalcitrant proteins, maximizing the productivity of hairy root cultures is essential. The aim of this study was to optimize a Brassica rapa rapa hairy root process for secretion of α-L-iduronidase (IDUA), a biologic of medical value. The process was first optimized with hairy roots expressing eGFP. For the biomass optimization, the highest biomass yields were achieved in modified Gamborg B5 culture medium. For the secretion induction, the optimized secretion media was obtained with additives (1.5g/l PVP + 1mg/l 2,4-D + 20.5g/l KNO ₃) resulting in 3.4 fold eGFP secretion when compared to the non-induced control. These optimized conditions were applied to the IDUA-expressing hairy root clone, confirming that the highest yields of secreted IDUA occurred when using the already defined additive combination. The functionality of the IDUA protein, secreted and intracellular, was confirmed with an enzymatic activity assay. A >150-fold increase of the IDUA activity was observed using an optimized secretion medium, compared with a non-induced medium. We have proven that our B. rapa rapa hairy root system can be harnessed to secrete recalcitrant proteins, illustrating the high potential of hairy roots in plant molecular farming.