The supply sources for most LSD are believed to be centered in northern California. At the wholesale production and trafficking levels, LSD remains tightly controlled by relatively small California-based organizations that have successfully evaded drug law enforcement operations for more than two decades. Mid-level distribution networks generally consist of individuals who have known each other for many years. However, increasing numbers of individuals have tried to manufacture LSD over the past several years. Public and private mail systems appear to be the primary distribution methods. LSD is relatively inexpensive; street dosages cost an average of $5 and as little as $1 or $2. The potency is 20-80 micrograms per dosage unit, considerably below the 100-200 micrograms during the 1960's and early 1970's. An estimated 13.2 million people 12 years old or older have used LSD at least once, compared to 8.1 million in 1985. Use among high school seniors in the class of 1993 was the highest since 1985. The number of hospital emergencies related to LSD remains low compared to other major illegal drugs of abuse. Footnotes, photographs, and map