(lethal dose 50) The dose at which 50% of laboratory animals die within days to weeks.
Dose required to kill 50% of laboratory test animals.
Dose which kills half of the tested population.
Stands for lethal dose 50, an index of acute toxicity established by dosing animals (usually rats) until 50% of the test population dies. Doses may be established for oral, dermal or inhalation exposures eg LE50(concentration).
median lethal dose.
Median Lethal Dose. Statistically derived single dose that can be expected to cause death in 50% of dosed animals
That dose of a compound which causes death in 50% of the organisms to which it has been administered. Routine use of LD50 tests is now being replaced by more sensitive (and less wasteful) methods.
Lethal dose of a substance that will kill 50% of all organisms exposed to that dose.
See LDn
The value of a given experimental variable required to cause 50% mortality. 
n. median lethal dose; a quantity or concentration of toxin at which half of the test subjects to whom it is administered are killed by its effects