A study of Greek speakers' ability to understand and produce two varieities of codes--Katharevousa (K) and Demotic (D)--is reported. The investigation was undertaken to provide evidence supporting or refuting the Greek government's decision to legislate Demotic as the official language of the country. A sample of 545 informants were tested with a reading comprehension test and a cloze procedure production test on three texts in either of the two variations. A significantly higher performance in favor of D indicated that D alone is the code that can function adequately as an effective means of communication, supporting the government's policy. In addition, the weakening of performance in K was found to be strongly evident in the poor performance of the subjects, based on the higher proportion and severity of errors committed. The pattern of interference appears to be in one direction only, from D to K. Based on these findings, it is concluded that any moves to reintroduce K are bound to result in failure. (MSE)