All the major tobacco companies have repeatedly denied that they manipulate or control nicotine levels or design their cigarettes to deliver specific levels of the chemical.

But thousands of internal memorandums released on Friday by the companies provide a portrait of an industry obsessed with nicotine, its physiological and pharmacological effects and the myriad ways in which it might be controlled and altered while being delivered to the smoker.Over the past three decades, the tobacco industry poured millions of dollars and thousands of research hours into exploring how to "manipulate," "control" and "augment" nicotine, the documents show. The methods explored included treating nicotine with ammonia; adding other chemicals; new filter and cigarette paper designs, and direct addition of nicotine, according to the documents.

The documents were initially collected by lawyers for Minnesota for use in a lawsuit against the nation's four largest cigarette companies: Philip Morris, RJ Reynolds Tobacco Co., Lorillard Tobacco Co. and Brown & Williamson Tobacco.

The cigarette makers had initially resisted disclosing the records. But last month they agreed to disclose some of the records in an apparent bid to improve prospects for congressional passage of the $368.5 billion tobacco settlement proposal reached in June between the industry and 40 state attorneys general. The documents were posted Friday on the Internet.

According to the documents, Philip Morris, for example, apparently conducted a long line of experiments intended to examine the relationship between the alkalinity of smoke, nicotine delivery and smoker response.

One 1990 research memorandum states, "We have shown that there are optimal nicotine deliveries for producing the most favorable physiological and behavioral responses."