Single-molecule detection (SMD) is becoming more and more popular in the sc
ientific community and is on the threshold to become a technique for labora
tory use. Therefore, conceivable applications as well as optimized conditio
ns for SMD will be discussed. To point out the possibilities of SMD, the si
gnal-to-background ratio and the detection efficiency, in combination with
the probability of misclassification, will be contemplated.