  A multi-transition 3$ $mm molecular line single-pointing and mapping survey
was carried out towards 29 massive star-forming cores in order to search for
the signature of inward motions. Up to seven different transitions, optically
thick lines HCO$^+$(1-0), CS(2-1), HNC(1-0), HCN(1-0), $^{12}$CO(1-0) and
optically thin lines C$^{18}$O(1-0), $^{13}$CO(1-0) were observed towards each
source. The normalized velocity differences ($\delta$V$_{\rm CS}$,
$\delta$V$_{\rm HCO^{+}}$) between the peak velocities of optically thick lines
and optically thin line C$^{18}$O(1-0) for each source were derived. Prominent
inward motions are probably present in either HCO$^+$(1-0) or CS(2-1) or
HNC(1-0) observations in most sources. Our observations show that there is a
significant difference in the incidence of blue shifted line asymmetric line
profiles between CS(2-1) and HCO$^+$(1-0). The HCO$^+$(1-0) shows the highest
occurrence of obvious asymmetric feature, perhaps owing to different optical
depth between CS(2-1) and HCO$^+$(1-0). HCO$^+$(1-0) appears to be the best
inward motion tracer. The mapping observations of multiple line transitions
enable us to identify six strong infall candidates G123.07-6.31, W75(OH),
S235N, CEP-A, W3(OH), NGC7538. The infall signature is extended up to a linear
scale $>0.2 \:$pc.
