A general review of molecular sieve zeolites precedes a more specialised account of the properties of the zeolites omega and erionite. It is these relatively unstudied zeolites which have been selected for a entailed catalytic characterisation utilising the isomerisation of the n-butenes and the methyl substituted cyclopropanes as test reactions. The resulting product distributions for each zeolite were indicative of carbonium ion type mechanisms. A study of the reaction of specifically labelled deuteropropene, CD 2=CH-CH3, on the catalysts confirmed this mechanism and moreover, demonstrated that the intermediate carbonium ion was formed in an associative manner involving Bronsted acid sites. A gravimetric study of the sorption of reactant and product molecules into the zeolites was also carried out. The wide pore zeolite omega exhibited rapid sorption and desorption of all three n-butenes and methylcyclopropane. Conversely, the rates of sorption of the n-butenes into erionite were a function of their dipole moments and structures, the order trans but-2-ene > but-l-ene > cis but-2-ene being observed. Furthermore, the sorption rates shown by erionite were dependent on the ionic composition of the erionite sample.