The properties of co- and terpolymers (physical, mechanical, chemical, biocompatibility, etc.) strongly depend on their microstructural details. In the course of our research work on biomaterials that feature intrinsic radiopacity, we became interested in the microstructural details of co- and terpolymers of methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), and 2-(2’-iodobenzoyl)ethyl methacrylate (1) or 2-(4’-iodobenzoyl)ethyl methacrylate (2). A new method, based on H-1-NMR at 400 MHz, was used to study the copolymerization reactions 1 + HEMA, 1 + MMA, 2 + HEMA, and 2 + MMA. This method was found to be convenient, fast, and accurate, and it is put forward that this approach can also be applied to study other copolymerization reactions. The results, obtained with the error-invariables method (EVM), are as follows : 1 + HEMA, r(1) = 1.09 +/- 0.14, r(HEMA) = 1.12 +/- 0.06; 1 + MMA, r(1) = 0.54 +/- 0.12, r(MMA) = 0.67 +/- 0.06; 2 + HEMA, r(2) = 2.18 +/- 0.72, r(HEMA) = 2.29 +/- 0.38; 2 + MMA, r(2) = 0.93 +/- 0.32, r(MMA) = 0.90 +/- 0.13. Based on these data, a triad analysis was performed. It is concluded that all four copolymerizations afford random-type macromolecules. Therefore, it is most likely that terpolymers consisting of 1 or 2, HEMA, and MMA will also have a random character. This conclusion is of interest, since it gives a better insight into the different biochemical and physicochemical properties of this type of co-/terpolymers. The results imply that random copolymers, built-up from a hydrophilic and a hydrophobic component, can also exhibit low thrombogenicity; this is in line with recent studies by Mathew et al. (Biomaterials 1993, 14, 57).