  The ARGO-YBJ experiment will be installed at YangBaJing Cosmic Ray Laboratory
(Tibet, P.R. China), 4300 m a.s.l. . It consists of a full coverage of about
10^4 m^2 realized with RPC chambers.
  A small carpet of about 50 m^2 has been operated at YangBaJing in order to
check the RPC performance in these high altitude conditions.
  Results concerning efficiency and time resolution are reported.
