The strategy, as regards the layout of any clinical study on Alzheimer's disease (AD) which aspires to an evaluation of the therapeutical efficiency of a drug, must take as its starting point a clear specification of the criteria of improvement and of how such criteria are to be quantified. The measuring instruments of therapeutical efficiency can be divided into two main groups: instruments for analysing the biological parameters of the illness and instruments which analyse functional efficiency. Between the latter, there are three types of basic tools: 1. Tests which allow psychopathological clinical changes to be evaluated, such as a complete neuropsychological examination, an analysis of the global clinical impression, and a cognitive mini-test; 2. Psychometric tests which allow certain parameters to be quantified, such as, for example, the IQ co-efficient; 3. Scales which, by means of information supplied by care experts or by family members, allow the ability to carry out normal daily tasks to be quantified. The selection of the most suitable test as an instrument with which the criteria of improvement may be established has given rise to controversy and none have been found which, on their own, can fully guarantee the necessary requirements of objectivity, reproduceability, validity and homogeneity. Within these limits, the most suitable are held to be those which explore psychopathological changes and the data provided by an informer, together with the global clinical impression. The high number of tests and batteries that have been proposed for the evaluation of the therapeutic response indicates their lack of real efficiency. We would like to see the setting up of an international committee for the standardisation and definitive validation of the measuring instruments for cognitive deterioration, and thus establish--with precision, unanimity and a general consensus--what might be considered to be the most suitable criteria of improvement when evaluating therapeutic efficiency in Alzheimer's disease.