Quasi-periodic density structures are important mesoscale structures that constitute the slow solar wind. The associated periodicities play a fundamental role in the understanding of the release processes of solar coronal plasma and provide important constraints on models trying to understand the origin of the slow solar wind. However, observational restrictions have limited their study to coronagraph images near the Sun and in situ measurements at 1 AU, preventing a clear connection between in situ structures to their coronal sources. A first step toward a better understanding of this problem is the analysis of Helios measurements to probe the solar wind between 0.3 and 0.6 AU. Three instances of quasi-periodic density structures have been identified showing characteristic timescales of ≈31-33 minutes and ≈112-120 minutes. Using the mean radial bulk speed corresponding to the time intervals of the structures, the related radial lengthscales are derived showing a characteristic value of ≈120-150 RE
