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Arbuscular mycorrhizal fungi (AMF), which represent widespread and the most ancient symbiosis, cannot be grown outside the host plants like other fungi. The absence of an authentic pure culture creates a problem in their commercial production and study of symbiosis. Piriformospora indica isolated from desert soil of north-west India is similar to AM fungi. Like AMF, it has a broad and diverse spectrum, exerts plant growthpromoting effects on host plants, relieves stress conditions and acts as a tool for biological hardening of micro-propagated plants as well as biofertiliser and bioprotector. A similar behavior is shown by another fungus Sebacina vermifera. S. vermifera-inoculated plants flowered earlier, produced more flowers and matured more seed capsules than did non-inoculated plants. But the most important advantage of these two fungi over AMF is that they are facultative symbionts and can be easily cultivated axenically on a variety of synthetic media. Linum album is a perennial plant. Cell suspension cultures of this plant are able to produce lignans, which are derivatives of the general phenylpropanoid pathway. The main lignan in L. album is podophyllotoxin, which is used for the semi-synthetic production of the anti-tumor agents, etoposide, etopophos and teniposide. Lignans are defense molecules produced by plants in response to any pathogenic attack or under stress conditions by elicitation. To investigate the elicitation of lignan biosynthesis, the effect of culture filtrates of P. indica and S. vermifera on production of podophyllotoxin (PT) and 5-methoxypodophyllotoxin (5-MPT) was studied. Further, to investigate if the two fungi have some plant growth- promoting activity along with production of elicitors, which could activate biosynthetic pathway of PT production, both the fungi were individually co-cultivated with L. album in suspension cultures for different time periods and at different levels of fungal inoculums. The PT and 5-MPT content in both the cases were found to be significantly enhanced on co-culturing the fungi with the plant cells. The activity of phenylalanine ammonia lyase was observed to be related to the lignan accumulation indicating its role as the key enzyme of the phenylpropanoid pathway. The study resulted in lignan accumulation of 740 mg/L of culture broth with a very high productivity of 52 mg/ (L.d).