We present a search for electroweak production of single top quarks in the
electron + jets and muon + jets decay channels. The measurements use approx
imate to 90 pb(-1) of data from Run 1 of the Fermilab Tevatron collider, co
llected at 1.8 TeV with the D empty set detector between 1992 and 1995. We
use events that include a tagging muon, implying the presence of a b jet. t
o set an upper limit at the 95% confidence level on the cross section for t
he s-channel process p (p) over bar --> tb + X of 39 ph. The upper limit fo
r the t-channel process p (p) over bar --> tqb + X is 58 pb.