As the first part of the analysis of deverbal verb derivation in the Prussian Lithuanian texts up to the 17th century,  I investigated the relationship between the prefixed momentaneous verbs in the Gospels and Epistles and in the Catechism of Baltramiejus Vilentas. Based on an empirical study of the verbs in their contexts, I allocated each verb under investigation into the Vendler (1957) classes (state, activity, achievement, accomplishment) and annotated the verbs by valency. After this, I compared the momentaneous derived verbs with their attested unprefixed base verbs which mostly are of the mixed type. Morphologically, it turns out that the mixed verbs are to be seen as primary and not as derivatives as the formant (-ė- or -o-) of the infinitive stem might suggest since there are no attested primary verbs without the formant, e.g. *mokti, *moksta. The prefixed momentaneous verbs have the infix/sta-formant in the present stem, the prefix in all stems, and additionally no suffix in the infinitive stem in contrast to their base verbs.