  In this paper, we give a few results on the local behavior of harmonic
functions on the Sierpinski triangle - more precisely, of their restriction to
a side of the triangle. First we present a general formula that gives the
H\"older exponent of such a function in a given point. From this formula, we
deduce an explicit algorithm to calculate this exponent in any rational point,
and the fact that the derivative of such a function is always equal to 0,
infinity or undefined.
