  We report the discovery of broad Wolf-Rayet emission lines in the Multiple
Mirror Telescope (MMT) spectrum of the NW component of I Zw 18, the
lowest-metallicity blue compact dwarf (BCD) galaxy known. Two broad Wolf-Rayet
(W-R) bumps at the wavelengths $\lambda$4650 and $\lambda$5800 are detected
indicating the presence of WN and WC stars. The total numbers of WN and WC
stars inferred from the luminosities of the broad He II $\lambda$4686 and C IV
$\lambda$5808 lines are equal to 17(+/-)4 and 5(+/-)2, respectively. The W-R to
O stars number ratio is equal to about 0.02, in satisfactory agreement with the
value predicted by massive stellar evolution models with enhanced mass loss
rates. The WC stars in the northwest component of I Zw 18 can be responsible
for the presence of the nebular He II $\lambda$4686 emission line, however the
observed intensity of this line is several times larger than model predictions,
and other sources of ionizing radiation at wavelengths shorter than 228\AA are
necessary.
