From May till October 1999, 1-year-old birch seedlings were grown in a greenhouse in a substrate (forest soil under a birch tree + perlite, 1:1), without and with added aluminium chloride (40 and 160 mg Al dm^-3). The added aluminium chloride inhibited the growth of seedlings, especially of their roots. At the end of the experiment the substrate treated with aluminium chloride contained more Al and Cl than the control. In comparison with control plants, the treated plants did not differ in assimilation of Ca, Mg and K ions, but their leaves and roots contained more Al. Disease symptoms on leaves of treated seedlings were similar to those observed on birch trees growing in a contaminated area (near a phosphate fertilizer factory in Luboń). From collected birch leaves, symptomatic and asymptomatic, 18 species of fungi were isolated. From leaves of treated seedlings and of trees growing in the polluted area some fungal species were isolated more often than from control seedlings. Those species included: Aureobasidium pullulans, Hormonema dematioides, Alternaria alternata, and Cladosporium herbarum.