2-Thio-3-chloroacrylamides undergo 1,3-dipolar cycloaddns. with diazoalkanes leading to a series of novel pyrazolines and pyrazoles. The mechanistic and synthetic features of the cycloaddns. to the 2-thio-3-chloroacrylamides at both the sulfide and sulfoxide levels of oxidn. are rationalized on the basis of the nature of the substituents.