The gas-phase reactivity of W (a S-7(3) and a D-5(J)) with C2H4 and NH3 at room temperature was investigated using a time-resolved laser,induced fluorescence (LIF) spectroscopy. Tungsten atoms were produced by a 266-nm multiphoton decomposition (MPD) Of W(CO)(6). The reactant pressure dependence of the pseudo-first-order depletion rates of W (a S-7(3)) could allow an estimation of the pseudo-second-order depletion rate constant of W (a S-7(3)), (4.5 +/- 0.5) x 10(-10) cm(3) molecule(-1) s(-1) for C2H4 and (0.73 +/- 0.10) x 10(-10) for NH3 at 6.0-Torr total pressure with an Ar buffer. A simulation of the transient curves based on a modification of the observed apparent decay rate constants, involving nearby a D-5(J) states in the presence of C2H4 and NH3, allowed us to separately estimate the contribution of the chemical quenching (W (a S-7(3)) + R --> product(s)) and the physical quenching (W (a S-7(3)) + R --> W (a D-5(1)) + R) processes. In the case of C2H4, chemical quenching appeared to dominate over the physical quenching, while the physical quenching was the main depletion process in the case of NH3. The large reactivity of the W (a S-7(3)) state not only for C2H4, but also for NH3, is discussed in terms of the relativistic effects.