Six children were studied from the age of 0;6 to 1;6 in order to chart their developing comprehension vocabularies from the first to the 100th word. Observational data were used in the first instance to identify newly comprehended words and then controlled testing was carried out for each word to confirm and expand the observational data. Comprehension of words was divided into four categories – object names, context-bound object words, action words and personal names. The relative frequency of the different categories of word was found to change with the size of the comprehension vocabulary as personal names decreased in importance and both object names and action words became increasingly more common. There was considerable variation among the six children especially in the proportion of object names and action words that they understood but vocabulary composition became highly stable between 60 and 100 words.