public function syncLead($key, $attrs)
    {
        // Build array of Attribute objects
        $attrArray = array();
        foreach ($attrs as $attrName => $attrValue) {
            $a = new Attribute();
            $a->attrName = $attrName;
            $a->attrValue = $attrValue;
            $attrArray[] = $a;
        }

        $aryOfAttr = new ArrayOfAttribute();
        $aryOfAttr->attribute = $attrArray;

        // Build LeadRecord
        $leadRec = new LeadRecord();
        $leadRec->leadAttributeList = $aryOfAttr;

        // Set the unique lead key.
        if (is_numeric($key)) {
            $leadRec->Id = $key; // Marketo system ID.
        } else {
            $leadRec->Email = $key; // TODO - Add email format validation - should be SMTP email address.
        }

        // Build API params
        $params = new paramsSyncLead();
        $params->leadRecord = $leadRec;

        $params->returnLead = false; // Don't return the full lead record - just the ID.

        $options = array();

        $authHdr = $this->_getAuthenticationHeader();

        try {
            $success = $this->connection->__soapCall('syncLead', array(
                $params
            ), $options, $authHdr);
            $resp = $this->connection->__getLastResponse();
        } catch (SoapFault $ex) {
            // error_log(print_r($ex, true));
            $ok = false;
            $errCode = 1;
            $faultCode = null;
            if (! empty($ex->detail->serviceException->code)) {
                $errCode = $ex->detail->serviceException->code;
            }
            if (! empty($ex->faultCode)) {
                $faultCode = $ex->faultCode;
            }
            switch ($errCode) {
                case mktWsError::ERR_LEAD_SYNC_FAILED:
                    // Retry once and handle error if retry fails.
                    break;
                default:
            }
            if (! $ok) {
                if ($faultCode != null) {
                    if (strpos($faultCode, 'Client')) {
                        // This is a client error. Check the other codes and handle.
                    } else
                        if (strpos($faultCode, 'Server')) {
                            // This is a server error. Call Marketo support with details.
                        } else {
                            // W3C spec has changed :)
                            // But seriously, Call Marketo support with details.
                        }
                } else {
                    // Not a good place to be.
                }
            }
        } catch (Exception $ex) {
            $msg = $ex->getMessage();
            $req = $this->connection->__getLastRequest();
            echo "Error occurred for request: $msg\n$req\n";
            var_dump($ex);
            exit(1);
        }

        return $success;
    }