  We present an approach for analysing the morphology and physical properties
of Hi features near giant OB asso- ciations in M33, in the context of a model
whereby the Hi excess arises from photodissociation of the molecular gas in
remnants of the parent Giant Molecular Clouds (GMCs). Examples are presented
here in the environs of NGC604 and CPSDPZ204, two prominent Hii regions in M33.
These are the first results of a detailed analysis of the environs of a large
number of OB associations in that galaxy. We present evidence for "diffusion"
of the far-UV radiation from the OB association through a clumpy remnant GMC,
and show further that enhanced CO(1-0) emission appears preferentially
associated with GMCs of higher volume density.
