The host specificity of E. cichoracearum from Zinnia elegans, Helianthus annuus, Inula helenium, Cerinthe major, Cucurbita pepo, and perennial cultivated Phlox paniculata, P. maculata, or their hybrids was tested by inoculation expts., using a technique of dusting conidia onto the exptl. plants first sprayed with distilled water. Observations were made on the 5th and 7th, 8th or 9th days after inoculation. Three forms of E. cichoracearum were demonstrated. The zinnia mildew infected_ Z. elegans, Z. pauciflora, Z. verticillata, Helianthus annuus, Arctium minus, A. nemorosum, Xanthium chinense, X. spinosum, X. strumarium, Mikania scandens, Hieracium alpinum, H. prenanthoides, Inula helenium, Carlina acaulis, Lactuca perennis, Cosmos sp., Scorzonera hispanica and Felicia amelloides of the Compositae; Salpiglossis sinnata of the Solanaceae, and Cerinthe major of the Boraginaceae. The phlox mildew was shown to be restricted to P. drummondii and the cultivated perennial phlox among the 36 spp. from 6 families inoculated. The cucurbit mildew was shown to be restricted to certain genera and spp. of the Cucurbitaceae, infection failing on spp. from the 6 other families inoculated.