The Laser Interferometer Space Antenna (LISA) guarantees the detection of gravitational waves by monitoring a handful of known nearby galactic binary systems, the so-called verification binaries. We consider the most updated information on the source parameters for the 30 more promising verification binaries. We investigate which of them are indeed guaranteed sources for LISA and estimate the accuracy of the additional information that can be extracted during the mission. Our analysis considers the two independent Michelson outputs that can be synthesized from the LISA constellation, and we model the LISA transfer function using the rigid adiabatic approximation. We carry out extensive Monte Carlo simulations to explore the dependency of our results on unknown or poorly constrained source parameters. We find that four sources—RXJ0806.3+1527, V407 Vul, ES Cet and AM CVn—are clearly detectable in one year of observation; RXJ0806.3+1527 should actually be observable in less than a week. For these sources LISA will also provide information on yet unknown parameters with an error between ≈1% and ≈10%. Four additional binary systems—HP Lib, 4U 1820-30, WZ Sge and KPD 1930+2752—might also be marginally detectable.