  We present deep spectrophotometry of several Hii regions in the nearby
low-mass spiral galaxies NGC 300 and M33. The data have been taken with UVES
and OSIRIS spectrographs attached to the 8m VLT and 10.4m GTC telescopes,
respectively. We have derived precise values of the physical conditions for
each object making use of several emission line-intensity ratios. In
particular, we have obtained direct determinations of the electron temperature
in all the observed objects. We detect pure recombination lines (RLs) of Cii
and Oii in several of the Hii regions, permitting to derive their C/H and C/O
ratios. We have derived the radial abundance gradient of O for each galaxy
making use of collisionally excited lines (CELs) and RLs, as well as the C and
N gradients using RLs and CELs, respectively. We obtain the first determination
of the C/H gradient of NGC 300 and improve its determination in the case of
M33. In both galaxies, the C/H gradients are steeper that those of O/H, leading
to negative C/O gradients. Comparing with similar results for other spiral
galaxies, we find a strong correlation between the slope of the C/H gradient
and M_V. We find that some Hii regions located close to the isophotal radius
(R_25) of NGC 300 and M33 show C/O ratios more similar to those typical of
dwarf galaxies than those of Hii regions in the discs of more massive spirals.
This may be related to the absence of flattening of the gradients in the
external parts of NGC 300 and M33. Finally, we find very similar N/H gradients
in both galaxies and a fair correlation between the slope of the N/H gradient
and M_V comparing with similar data for a sample of spiral galaxies.
