FARMAGUIDA, a databank of drugs marketed in Italy (2,596 pharmaceutical substances corresponding to 10,448 products), permits analysis of the nature and value of the drugs prescribed. It contains coded pharmaceutical and administrative information, an original classification, as well as indicators of the therapeutic status of each drug. The FARMAGUIDA classification was built hierarchically according to a three-level pattern: the first level (42 categories) corresponds to major pharmacological groups; the second level (157 groups) gathers drugs having similar clinical indications and/or pharmacological actions; and the third level (246 subgroups) classifies drugs according to chemical structure and/or the mechanism of action. Drugs not falling into well-established pharmacotherapeutic criteria (e.g. neurotropics or liver protectants) are classified into separate subgroups. Two larger groupings were also formulated: THER (11 headings), a utilization-oriented arrangement in which each heading also contained the corresponding placebo-like drugs, and PHARM (14 headings), a rational pharmacological arrangement, in which all placebo-like drugs were relegated into a separate set. The following quality indicators were created: DOC, which defines five degrees of documentation of clinical efficacy according to major textbooks of pharmacology and therapeutics; CLASS, which groups DOC values for a more simple evaluation of prescription data; PREP, which distinguishes monocomponent preparations from fixed-dose combinations, and also provides coded information about the rationale for the combination; HOSP, which hallmarks drugs that should be reserved for in-patients, e.g. anti-pseudomonal antibiotics. The composition of the list of reimbursable drugs, the Italian National Formulary (NF; 5782 products in 1990) was analyzed according to the FARMAGUIDA classification and indicators.(ABSTRACT TRUNCATED AT 250 WORDS)