Most of you know that elastin is a connective tissue protein, although most of you probably don’t want to admit it. Elastin has a more restricted distribution than collagen does and, of course, therefore there are less people working on elastin than on collagen. Nevertheless, I think that in the last few years people are beginning to realize that it has tremendous application to a number of medical problems, and particularly in the relationship to lung disease and arterial vessel disease. Figure 1 is taken from a twenty-day old chick embryo lung. Now, most of you who are fascinated with hard, rigid molecules don’t even want to admit that this rather amorphous looking material is a fibrous protein. The elastic fiber itself is composed of two components: amorphous elastin, which I am going to talk about exclusively this morning and which we ordinarily think of when we use the word elastin; and another component, the so-called microfibrillar component which has definitely a different composition from the amorphous component which is rich in glycine, alanine, proline, valine and other hydrophobic amino acids. This microfibrillar material on the outside is much more acidic, and it apparently has a lot of cysteine in it.’ Very little is actually known about the microfibrillar component. I think, in summary, it is fair to say that a lot of the reports that have come out in the past few years, allegedly describing microfibrillar component, are doubtful. I think there truly has to be a lot of work done on that particular component. What is known about the chemical and physical structure of the elastin molecule? What are our best guesses as to how it is organized in the fiber? In most pictures of elastin one sees very little structure. This is true when one is doing ordinary sections and ordinary types of staining. However, if elastin is prepared under certain conditions such as in the classical Lansing way by boiling a tissue in 0.1N sodium hydroxide and operationally defining whatever is left as elastin, this remaining material, when negatively stained, possesses a fibrillar structure as has been reported by a number of investigators. Figure 2 is taken from a picture of Lorenzo Gotte’ who has been one of the primary advocates of an internal fibrillar structure of that amorphous component. I think it is fair to say that it is still an ongoing controversy whether this fibrillar structure is an artifact. People have suggested that it is some kind of contaminant that has been floating around and has been picked up and put into the EM, or that this is an artifact resulting from the way in which the specimen has been prepared. These fibrillar diameters have varied from the smallest one, about fifteen Angstroms, up to fifty Angstroms or so. Based upon this kind of EM studies, people have suggested that there is some kind of internal structure. This implies some ordering of the molecules. Unfortunately, how