  We characterize the molecular environment of candidate massive young stellar
objects (MYSOs) signposted by methanol masers. Single pixel observations of 10
transitions of HCO^+, CO and CS isotopomers were carried out, using the IRAM
30m telescope. We studied a sample of 28 targets for which the 6.7GHz maser
emission positions are known with a sub-arcsecond accuracy. The systemic
velocity inferred from the optically thin lines agrees within 3km/s with the
central velocity of the maser emission for most of the sources. About 64% of
the sources show line wings in one or more transitions of CO, HCO^+ and CS
species, indicating the presence of molecular outflows. Comparison of the
widths of line wings and methanol maser emission suggests that the 6.7GHz maser
line traces the environment of MYSO of various kinematic regimes. Therefore
conditions conducive for the methanol maser can exist in the inner parts of
molecular clouds or circumstellar discs as well as in the outer parts
associated with molecular outflows. Calculations of the physical conditions
based on the CO and HCO^+ lines and the CS line intensity ratios refine the
input parameters for maser models.
