LSD is still readily available in the United States as a street drug of abuse. Emergency physicians may be called on to diagnose acute LSD intoxication in cases in which the history is unavailable. The typical LSD intoxication syndrome causes marked illusions of color and sound, along with a feeling of "cosmic awareness." True hallucinations only occasionally occur; the pupils invariably are massively dilated. The diagnosis may be very difficult to establish when other drugs, particularly those causing coma, are present. The toxicology laboratory can now easily detect LSD by radioimmunoassay.