On modelling the kinetics of dissolution, two variants of Weibull equation in a two-parameter or tree-parameter form are used, the estimations of their parameters not being quite comparable. The introductory part of the paper sums up four variants of the equation and chracterized their relationship to granulometric Rosin–Rammler–Sperling equation. The kinetics of liberation of pilocarpinium chloride from lyophilized lamellae with graded amounts of hydroxypropylmethylcellulose is expressed by the above-mentioned equations and their parameters are compared. The conclusions generally discusses the usability of equations and their correct interperetation in modelling dissolution of active ingrediens from dosage forms.

        Key words: Weibull equation – dissolution kinetics – hydroxypropylmethylcellulose – pilocarpinium chloride