The role of algae in soils and the factors that limit these communities has received much attention worldwide, yet results have been inconclusive. Furthermore, New Zealand studies on soil algae have been few, with a limited range of soils being studied. The aims of the present study were to: Further knowledge of diversity and abundance of algae in New Zealand soils and particularly those of subalpine hillside slopes. Examine factors controlling growth of algae in hillside mineral soils. Combine field observations with field and laboratory experiments to understand factors controlling algal growth, particularly the effects of water and nutrients. Investigate whether the community on bare mineral hillside soils is distinct from other soils within the study area at Cass. This study isolated algae from 37 genera, 28 of which were new records for New Zealand. Twenty-two algae were isolated as unialgal cultures with the remainder identified from moist plate enrichment cultures. This showed the lack of knowledge within this country as all genera have commonly been isolated from soils elsewhere. Most common in hillside mineral soils were Eustigmatos spp. This genus was not found in grassland soils where Pseudococcomyxa sp. was dominant. Cyanophytes were rare in dilution plates but common in moist plate enrichment cultures, while occasional dead diatom frustules were the only evidence of this group of algae. From field observations combined with laboratory and field experiments, nutrients and water were found to be limiting algal growth on hillside mineral soils. In the field, natural communities increased abundance with nutrient additions, while laboratory experiments increased growth of Eustigmatos sp., Oscillatoria sp. and Klebsormidium sp. after additions of water alone and with added mineral nutrients. Light intensity, soil temperature, sulphate concentrations and inhibitory substances in soil beneath Leptospermum scoparium are also suggested to be controlling algal growth at Cass. Insufficiencies in methods for studying soil algae led to some inconclusive results. These problems are outlined and further research directions are suggested.