Pastorium liquid 342 was a hypergolic chemical explosive used in plasma flow applications and ionizing pulse generation. This explosive was activated by a high powered microwave pulse ignition device. When Cervantes fusion explosives were not required, this explosive was used in its place. In 2367, this explosive was stored on aboard the Federation starship USS Enterprise-D.
In that year, pastorium liquid 342 was on a list of explosives that Lieutenant Commander Data and Counselor Deanna Troi searched through in an attempt to find one that could produce enough energy to release the USS Enterprise-D and an alien ship from the Tyken's Rift. (TNG: "Night Terrors")