  We report a study of the superconducting pairing of the noncentrosymmetric
La$_{4}$Be$_{33}$Pt$_{16}$ alloy using muon-spin rotation and relaxation
($\mu$SR) technique. Below $T_c = 2.4$ K, La$_{4}$Be$_{33}$Pt$_{16}$ exhibits
bulk superconductivity (SC), here characterized by heat-capacity and
magnetic-susceptibility measurements. The temperature dependence of the
superfluid density $\rho_\mathrm{sc}(T)$, extracted from the transverse-field
{\textmu}SR measurements, reveals a nodeless SC in La$_{4}$Be$_{33}$Pt$_{16}$.
The best fit of $\rho_\mathrm{sc}(T)$ using an $s$-wave model yields a magnetic
penetration depth $\lambda_0 = 542$ nm and a superconducting gap $\Delta_0 =
0.37$ meV at zero Kelvin. The single-gapped superconducting state is further
evidenced by the temperature-dependent electronic specific heat
$C_\mathrm{e}(T)/T$ and the linear field-dependent electronic specific-heat
coefficient $\gamma_\mathrm{H}(H)$. The zero-field $\mu$SR spectra collected in
the normal- and superconducting states of La$_{4}$Be$_{33}$Pt$_{16}$ are almost
identical, confirming the absence of an additional field-related relaxation
and, thus, of spontaneous magnetic fields below $T_c$. The nodeless SC combined
with a preserved time-reversal symmetry in the superconducting state prove that
the spin-singlet pairing is dominant in La$_{4}$Be$_{33}$Pt$_{16}$. This
material represents yet another example of a complex system showing only a
conventional behavior, in spite of a noncentrosymmetric structure and a
sizeable spin-orbit coupling.
