Maize attacked by the facultative biotrophic smut pathogen, Ustilago maydis (Basidomycetes) was ensiled in microsilos in two combinations of infected and non-infected plants, with or without biological (Polmasil) or chemical (Kemisile 2000) additives. The silage was subjected to chemical and microbiological analyses. The aerobic stability of the silage was tested. Ustilago maydis constituted up to 6.22% of the total yeast content (CFU g^-1) in the infected and 0.22% in the noninfected material. Silage made from infected plants had a higher content of fungi (6.45 vs 4.54), moulds (6.20 vs 4.54), and yeast (6.08 vs 3.71) expressed as log₁₀ CFU g^-1 as compared with noninfected plants. The use of the chemical additive decreased these effects. The contents of ochratoxin, zearalenone, and deoxynivalenol were low and did not change during the ensiling. The cytotoxicity test did reveal toxicity of silage from infected plants, however. It seems that the observed toxicity is the effect of toxins other than those assayed.