Phalaris minor (Retz.) has developed resistance against isoproturon in northern parIs of India. The biochemical and molecular mechanism(s) of resistance are not known so far. The present investigation was thus undertaken to predict some probable mechanism(s) by comparing the protein profiles of PS-ll and microsomal fractions for both biotypes when treated with isoproturon as well as RAPD profiles of the genomic DNA in isoproturon resistant and sensitive biotypes of P. minor. Protein profiles on gradient-PAGE were same for both biotypes as well as after treatment with different levels of isoproturon suggesting induction of no new protein(s) in PS-[] enriched and cytochrome P450 fractions. While RAPD analysis of genomic DNA showed difference in their banding patterns in two biotypes. This suggested that isoproturon resistance might be due to variation in many genes, which perhaps have regulatory roles.