Autotrophic organisms were found in house dust (mainly floordust) in the USA Bernstein & Safferman 1970; Holland et al. 1973, 1974; Richardson et al. 1974). These authors reported algae in the dust in high enough quantities to warrant allergological studies. This paper is devoted to autotrophic organisms in mattress dust. Direct examination of mattress dust collected in Nijmegen in September, 1974 showed algal filaments of 120 /un (Ulotrichales), in addition to diaspores of green and blue-green algae.