In this paper we study the following two problems: first, given a rati
onal parametrization P(z) = (p(1)(z), p(2)(z)) is an element of C(z)(2
) of a complex curve C in C-2, to determine algorithmically, if C has
an infinite number of real points (i.e. if the trace of C in R(2) is a
real curve). If this is the case, then we would like to find another
parametrization mapping of the same curve, but this time with real rat
ional functions. The solution to both problems is given here by a simp
le algorithm, requiring essentially just a gcd computation and a param
etrization of a real line or circle. On the other hand, the theoretica
l foundation for the algorithm seems more involved, relying on factori
zation properties of conjugate harmonic polynomials. The case of space
curves or curves over a higher dimensional space follows by a direct
generalization of our results or by considering the primitive element
theorem. (C) 1997 Academic Press Limited.