In this paper, we present an exploratory study of the pitch registers on the string quartets Opus 17, by Joseph Haydn, according to a quantitative approach. This subject is relevant because the pitch registers studies have revealed noteworthy issues in the Musical Analysis area, the statistical techniques help to detect musical subtleties with a small potential for bias, and because on this corpus, Haydn has established standards for the string quartet genre. The pitch registers study allowed us to identify relevant musical aspects in the repertoire, understand the role of extreme registers in the form segmentation, and observe the prominence of the development and second theme sections, and the feasibility of the quantitative methods. We present a brief theoretical foundation, the methodological framework, the results of the investigation on the quartets' instrument pitches, a discussion about these results, and the conclusions. Keywords: Pitch register, Quantitative analysis, Digital Musicology, String quartet, Joseph Haydn