Vertical muon intensity measured with MACRO at the Gran Sasso laboratory

The vertical underground muon intensity has been measured in the slant depth range 3200--7000 hg cm^-2 (standard rock) with the completed lower part of the MACRO detector at the Gran Sasso laboratory, using a large sample of data. These observations are used to compute the surface muon flux and the primary ``all-nucleon'' spectrum. An analysis of systematic uncertainties introduced by the interaction models in the atmosphere and the underground propagation of muons is presented. A comparison of our results with published data is also presented.