A new metabolite, identified as chaetoglobosin K, was isolated from cultures of Diplodia macrospora. It inhibited the growth of wheat coleoptiles and was toxic to day-old chicks with an LD50 between 25 and 62.5 mg/kg. The study reports the isolation of this new metabolite, its physical and chemical characteristics (e.g., molecular formula C34H40O5N2, melting point 264-266°C, spectral data consistent with a chaetoglobosin structure), and its biological effects: potent inhibition of wheat coleoptile growth (more active than some other cytochalasins at 10⁻⁴ and 10⁻⁵ M) and toxicity to day-old chicks with the observed LD50 range. Additionally, the concentration of the synthetic prostaglandin cloprostenol ("Estrumate") was measured in the milk of three cows after intramuscular dosing with [¹⁴C]cloprostenol; maximum milk concentration was 0.270 ng/mL at 4 h, declining to 0.002 ng/mL at 24 h, with excretion of radioactivity and cloprostenol proportion similar at 0.5 mg and 10 mg doses, demonstrating first-order clearance and similarity to endogenous PGF2α clearance time course.