Alarge proportion of the commonly used herbicidal substances were derived from that class of organic compounds somewhat loosely known as the substituted phenols. Many of these compounds, as well as their close relatives, have been reported to affect cell division in a number of ways. Since there appeared to be some confusion as to the type or types of effect as well as to the similarities between the effects of different members of the group, comparative studies of a number of compounds were undertaken. Two questions were considered: 1. are the cytological effects such as to suggest subtle biological hazards to organisms apparently not affected morphologically; and 2. is there a family resemblance in the cytological reaction category? Although neither question has been answered satisfactorily, the results of our studies to date are sufficiently suggestive to warrant reporting.