A search has been made for pairs and for single production of scalar l
eptoquarks of the first and second generations using a data sample of
392000 Z0 decays from the DELPHI detector at LEP 1. No signal was foun
d and limits on the leptoquark mass, production cross section and bran
ching ratio were set. A mass limit at 95% confidence level of 45.5 GeV
/c2 was obtained for leptoquark pair production. The search for the pr
oduction of a single leptoquark probed the mass region above this limi
t and its results exclude first and second generation leptoquarks D0 w
ith masses below 65 GeV/c2 and 73 GeV/c2 respectively, at 95% confiden
ce level, assuming that the D0lq Yukawa coupling alpha(lambda) is equa
l to the electromagnetic one. An upper limit is also given on the coup
ling alpha(lambda) as a function of the leptoquark mass m(D0).