ENThe aim of this paper is to measure the productivity of four distinct morphological constructions – verbal derivatives with prefixes nu-, pri-, į- and iš-. It is measured in quantitative way, employing the calculation methods of Harald Baayen (e.g., 2009). The primary foundations of these measurements are the so-called hapax legomena or simply hapaxes. The data for the investigation was gathered from morphologically lemmatized corpus “LithuanianWaC v2”. The analysis reveals that the prefix iš- is the most productive prefix in terms of realized and expanding productivity, and nu- – in terms of potential. The analysis raises a question – what factors could possibly explain, why constructions with one prefix are more productive compared to others? This leads to a partly confirmed hypothesis that suggests a correlation between productivity and the number of meanings associated with each prefix. However, this investigation extends beyond mere quantitative measurements. Hapaxes were categorized on the basis of their meanings. This categorization aimed to identify the most productive semantic models. Meanings were identified using cognitive analysis of semantics associated with these prefixes. Categorization shows that the most productive ones are prototypical spatial meanings, as well as those meanings which are based on metaphors including CONTAINER as a source domain. Furthermore, this paper raises discussion about the nature of hapaxes – which part of them consists of real neologisms and which represents just rarely used lexemes, and what are the tendencies and motivation of prefixal neologisms’ usage. Keywords: prefixes; productivity in language; cognitive semantics; conceptual metaphors; derivative morphology. [From the publication]