Lost circulation is still today one of the most costly problems for oil and gas operators. It may occur into permeable formations, depleted zones, induced or nature fractures and cavernous formations while drilling, cementing or during workover jobs in the well. This paper focus on the evaluation of bridging and reactive systems in remediating severe losses based on their performance in a dedicated experimental facility. Laboratory apparatus commonly used to evaluate lost circulation materials generally consist in modified API-fluid loss devices using slotted metal discs, ceramic discs or natural cores. These devices are suitable to simulate permeable formations or depleted zones, but they do not simulate severe lost circulation scenarios that occur in induced or nature fractures and in cavernous formations. For that reason, a specific laboratory apparatus was built, where the performance of several materials was evaluated and classified according to different severity levels. This paper summarizes the efficiency of available commercial bridging (granular, fibers and flakes) and reactive systems in remediating severe losses according to different severity levels imposed in the developed severe lost circulation apparatus. Besides commercial products alredy used to control losses, hydrated bentonite pellets have been evaluated as bridging material.