172 stream segments were sampled for the presence of Chaetophoraceae representatives among macroalgal communities from May to October in 1992-1993 and 1996-1997 in five natural regions (parts of biomes or selected geological areas) and one disturbed area of Sao Paulo State, southeastern Brazil (19°45'-21°25'S, 49°45'-51°30'W). This study is based on the examination of 97 samples, from which ten species of Chaetophoraceae were identified: Chaetophora attenuata, C. elegans, C. pisiformis, Draparnaldia mutabilis, Stigeoclonium amoenum, S. farctum, S. fasciculare, S. helveticum, S. lubricum and S. subsecundum. Chaetophora attenuata and S. subsecundum were reported for the first time for Brazil. For each species the following information was provided: description, diagnostic feature, illustration, list of populations examined, known distribution in Brazil and associated macroalgal species. Species of Chaetophora and Stigeoclonium were evaluated according to a new set of taxonomic criteria combining characters from prostrate and erect systems. The number of species found in streams from Silo Paulo State was relatively high when compared to other world regions; however, species abundance (% cover) showed lower values. No correlations between number and abundance of the family and environmental variables were found but the following combination of environmental parameters was the most closely related to the occurrence of Chaetophoraceae: higher temperatures and current velocity, intermediate specific conductance, oxygen saturation and turbidity and pH circumneutral. All species reported for Sao Paulo State can be considered as having wide geographical distribution, occurring in tropical and temperate regions of both hemispheres. members of Chaetophoraceae were found in all biomes/ regions. The most widespread species was C. elegans, occurring in four of the six regions investigated; on the other hand, 30 % of the total species were recorded in a single biome/ region. A reappraisal of specific identification in Chaetophoraceae is clearly needed. It should include a larger number of populations and habitats, and should embrace classical, morphological characters, as well as ultrastructural and molecular data.