Abstract: The present invention provides thiazolyl derivatives as new chemical substance represented by the general formula: ##STR1## wherein R.sup.1 stands for a lower alkyl group or a substituted or unsubstituted phenyl group, R.sup.2 for a hydrogen atom, a lower alkyl, lower alkoxy or lower alkylthio group, and R.sup.3 for a pyridyl or iso-oxazolyl group or a grouping of the general formula: ##STR2## processes for preparing same and pharmaceutical compositions containing the thiazolyl derivatives. More particularly, the present invention provides new thiazolyl derivatives which possess immuno-modulating activity and are thus therapeutically effective against immunodiseases such as chronic rheumatoid arthritis and also useful against viral diseases or for the immunotherapy of cancers and possess properties desirous as medicines with a slight toxicity, processes for preparing same and pharmaceutical compositions containing the new substance.